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.claude/skills/incremental-implementation/SKILL.md
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---
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name: incremental-implementation
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description: Delivers changes incrementally. Use when implementing any feature or change that touches more than one file. Use when you're about to write a large amount of code at once, or when a task feels too big to land in one step.
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---
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# Incremental Implementation
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## Overview
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Build in thin vertical slices — implement one piece, test it, verify it, then expand. Avoid implementing an entire feature in one pass. Each increment should leave the system in a working, testable state. This is the execution discipline that makes large features manageable.
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## When to Use
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- Implementing any multi-file change
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- Building a new feature from a task breakdown
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- Refactoring existing code
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- Any time you're tempted to write more than ~100 lines before testing
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**When NOT to use:** Single-file, single-function changes where the scope is already minimal.
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## The Increment Cycle
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```
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┌──────────────────────────────────────┐
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│ │
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│ Implement ──→ Test ──→ Verify ──┐ │
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│ ▲ │ │
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│ └───── Commit ◄─────────────┘ │
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│ │ │
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│ ▼ │
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│ Next slice │
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│ │
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└──────────────────────────────────────┘
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```
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For each slice:
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1. **Implement** the smallest complete piece of functionality
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2. **Test** — run the test suite (or write a test if none exists)
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3. **Verify** — confirm the slice works as expected (tests pass, build succeeds, manual check)
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4. **Commit** -- save your progress with a descriptive message (see `git-workflow-and-versioning` for atomic commit guidance)
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5. **Move to the next slice** — carry forward, don't restart
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## Slicing Strategies
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### Vertical Slices (Preferred)
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Build one complete path through the stack:
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```
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Slice 1: Create a task (DB + API + basic UI)
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→ Tests pass, user can create a task via the UI
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Slice 2: List tasks (query + API + UI)
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→ Tests pass, user can see their tasks
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Slice 3: Edit a task (update + API + UI)
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→ Tests pass, user can modify tasks
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Slice 4: Delete a task (delete + API + UI + confirmation)
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→ Tests pass, full CRUD complete
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```
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Each slice delivers working end-to-end functionality.
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### Contract-First Slicing
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When backend and frontend need to develop in parallel:
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```
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Slice 0: Define the API contract (types, interfaces, OpenAPI spec)
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Slice 1a: Implement backend against the contract + API tests
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Slice 1b: Implement frontend against mock data matching the contract
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Slice 2: Integrate and test end-to-end
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```
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### Risk-First Slicing
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Tackle the riskiest or most uncertain piece first:
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```
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Slice 1: Prove the WebSocket connection works (highest risk)
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Slice 2: Build real-time task updates on the proven connection
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Slice 3: Add offline support and reconnection
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```
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If Slice 1 fails, you discover it before investing in Slices 2 and 3.
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## Implementation Rules
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### Rule 0: Simplicity First
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Before writing any code, ask: "What is the simplest thing that could work?"
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After writing code, review it against these checks:
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- Can this be done in fewer lines?
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- Are these abstractions earning their complexity?
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- Would a staff engineer look at this and say "why didn't you just..."?
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- Am I building for hypothetical future requirements, or the current task?
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```
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SIMPLICITY CHECK:
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✗ Generic EventBus with middleware pipeline for one notification
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✓ Simple function call
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✗ Abstract factory pattern for two similar components
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✓ Two straightforward components with shared utilities
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✗ Config-driven form builder for three forms
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✓ Three form components
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```
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Three similar lines of code is better than a premature abstraction. Implement the naive, obviously-correct version first. Optimize only after correctness is proven with tests.
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### Rule 0.5: Scope Discipline
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Touch only what the task requires.
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Do NOT:
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- "Clean up" code adjacent to your change
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- Refactor imports in files you're not modifying
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- Remove comments you don't fully understand
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- Add features not in the spec because they "seem useful"
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- Modernize syntax in files you're only reading
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If you notice something worth improving outside your task scope, note it — don't fix it:
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```
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NOTICED BUT NOT TOUCHING:
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- src/utils/format.ts has an unused import (unrelated to this task)
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- The auth middleware could use better error messages (separate task)
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→ Want me to create tasks for these?
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```
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### Rule 1: One Thing at a Time
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Each increment changes one logical thing. Don't mix concerns:
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**Bad:** One commit that adds a new component, refactors an existing one, and updates the build config.
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**Good:** Three separate commits — one for each change.
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### Rule 2: Keep It Compilable
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After each increment, the project must build and existing tests must pass. Don't leave the codebase in a broken state between slices.
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### Rule 3: Feature Flags for Incomplete Features
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If a feature isn't ready for users but you need to merge increments:
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```typescript
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// Feature flag for work-in-progress
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const ENABLE_TASK_SHARING = process.env.FEATURE_TASK_SHARING === 'true';
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if (ENABLE_TASK_SHARING) {
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// New sharing UI
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}
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```
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This lets you merge small increments to the main branch without exposing incomplete work.
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### Rule 4: Safe Defaults
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New code should default to safe, conservative behavior:
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```typescript
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// Safe: disabled by default, opt-in
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export function createTask(data: TaskInput, options?: { notify?: boolean }) {
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const shouldNotify = options?.notify ?? false;
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// ...
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}
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```
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### Rule 5: Rollback-Friendly
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Each increment should be independently revertable:
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- Additive changes (new files, new functions) are easy to revert
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- Modifications to existing code should be minimal and focused
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- Database migrations should have corresponding rollback migrations
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- Avoid deleting something in one commit and replacing it in the same commit — separate them
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## Working with Agents
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When directing an agent to implement incrementally:
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```
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"Let's implement Task 3 from the plan.
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Start with just the database schema change and the API endpoint.
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Don't touch the UI yet — we'll do that in the next increment.
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After implementing, run `npm test` and `npm run build` to verify
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nothing is broken."
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```
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Be explicit about what's in scope and what's NOT in scope for each increment.
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## Increment Checklist
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After each increment, verify:
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- [ ] The change does one thing and does it completely
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- [ ] All existing tests still pass (`npm test`)
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- [ ] The build succeeds (`npm run build`)
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- [ ] Type checking passes (`npx tsc --noEmit`)
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- [ ] Linting passes (`npm run lint`)
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- [ ] The new functionality works as expected
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- [ ] The change is committed with a descriptive message
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**Note:** Run each verification command after a change that could affect it. After a successful run, don't repeat the same command unless the code has changed since — re-running on unchanged code adds no information.
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## Common Rationalizations
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| Rationalization | Reality |
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|---|---|
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| "I'll test it all at the end" | Bugs compound. A bug in Slice 1 makes Slices 2-5 wrong. Test each slice. |
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| "It's faster to do it all at once" | It *feels* faster until something breaks and you can't find which of 500 changed lines caused it. |
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| "These changes are too small to commit separately" | Small commits are free. Large commits hide bugs and make rollbacks painful. |
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| "I'll add the feature flag later" | If the feature isn't complete, it shouldn't be user-visible. Add the flag now. |
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| "This refactor is small enough to include" | Refactors mixed with features make both harder to review and debug. Separate them. |
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| "Let me run the build command again just to be sure" | After a successful run, repeating the same command adds nothing unless the code has changed since. Run it again after subsequent edits, not as reassurance. |
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## Red Flags
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- More than 100 lines of code written without running tests
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- Multiple unrelated changes in a single increment
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- "Let me just quickly add this too" scope expansion
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- Skipping the test/verify step to move faster
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- Build or tests broken between increments
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- Large uncommitted changes accumulating
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- Building abstractions before the third use case demands it
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- Touching files outside the task scope "while I'm here"
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- Creating new utility files for one-time operations
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- Running the same build/test command twice in a row without any intervening code change
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## Verification
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After completing all increments for a task:
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- [ ] Each increment was individually tested and committed
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- [ ] The full test suite passes
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- [ ] The build is clean
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- [ ] The feature works end-to-end as specified
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- [ ] No uncommitted changes remain
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@@ -0,0 +1,160 @@
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# Accessibility Checklist
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Quick reference for WCAG 2.1 AA compliance. Use alongside the `frontend-ui-engineering` skill.
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## Table of Contents
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- [Essential Checks](#essential-checks)
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- [Common HTML Patterns](#common-html-patterns)
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- [Testing Tools](#testing-tools)
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- [Quick Reference: ARIA Live Regions](#quick-reference-aria-live-regions)
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- [Common Anti-Patterns](#common-anti-patterns)
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## Essential Checks
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### Keyboard Navigation
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- [ ] All interactive elements focusable via Tab key
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- [ ] Focus order follows visual/logical order
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- [ ] Focus is visible (outline/ring on focused elements)
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- [ ] Custom widgets have keyboard support (Enter to activate, Escape to close)
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- [ ] No keyboard traps (user can always Tab away from a component)
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- [ ] Skip-to-content link at top of page - visible (at least) on keyboard focus
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- [ ] Modals trap focus while open, return focus on close
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### Screen Readers
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- [ ] All images have `alt` text (or `alt=""` for decorative images)
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- [ ] All form inputs have associated labels (`<label>` or `aria-label`)
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- [ ] Buttons and links have descriptive text (not "Click here")
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- [ ] Icon-only buttons have `aria-label`
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- [ ] Page has one `<h1>` and headings don't skip levels
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- [ ] Dynamic content changes announced (`aria-live` regions)
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- [ ] Tables have `<th>` headers with scope
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### Visual
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- [ ] Text contrast ≥ 4.5:1 (normal text) or ≥ 3:1 (large text, 18px+)
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- [ ] UI components contrast ≥ 3:1 against background
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- [ ] Color is not the only way to convey information
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- [ ] Text resizable to 200% without breaking layout
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- [ ] No content that flashes more than 3 times per second
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### Forms
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- [ ] Every input has a visible label
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- [ ] Required fields indicated (not by color alone)
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- [ ] Error messages specific and associated with the field
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- [ ] Error state visible by more than color (icon, text, border)
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- [ ] Form submission errors summarized and focusable
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- [ ] Known fields use autocomplete (for example `type="email" autocomplete="email"`)
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### Content
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- [ ] Language declared (`<html lang="en">`)
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- [ ] Page has a descriptive `<title>`
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- [ ] Links distinguish from surrounding text (not by color alone)
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- [ ] Touch targets ≥ 44x44px on mobile
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- [ ] Meaningful empty states (not blank screens)
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## Common HTML Patterns
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### Buttons vs. Links
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```html
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<!-- Use <button> for actions -->
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<button onClick={handleDelete}>Delete Task</button>
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<!-- Use <a> for navigation -->
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<a href="/tasks/123">View Task</a>
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<!-- NEVER use div/span as buttons -->
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<div onClick={handleDelete}>Delete</div> <!-- BAD -->
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```
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### Form Labels
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```html
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<!-- Explicit label association -->
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<label htmlFor="email">Email address</label>
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<input id="email" type="email" required />
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<!-- Implicit wrapping -->
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<label>
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Email address
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<input type="email" required />
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</label>
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<!-- Hidden label (visible label preferred) -->
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<input type="search" aria-label="Search tasks" />
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```
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### ARIA Roles
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```html
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<!-- Navigation -->
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<nav aria-label="Main navigation">...</nav>
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<nav aria-label="Footer links">...</nav>
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<!-- Status messages -->
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<div role="status" aria-live="polite">Task saved</div>
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<!-- Alert messages -->
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<div role="alert">Error: Title is required</div>
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<!-- Modal dialogs -->
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<dialog aria-modal="true" aria-labelledby="dialog-title">
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<h2 id="dialog-title">Confirm Delete</h2>
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...
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</dialog>
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<!-- Loading states -->
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<div aria-busy="true" aria-label="Loading tasks">
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<Spinner />
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</div>
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```
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### Accessible Lists
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```html
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<ul role="list" aria-label="Tasks">
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<li>
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<input type="checkbox" id="task-1" aria-label="Complete: Buy groceries" />
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<label htmlFor="task-1">Buy groceries</label>
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</li>
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</ul>
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```
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## Testing Tools
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```bash
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# Automated audit
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npx axe-core # Programmatic accessibility testing
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npx pa11y # CLI accessibility checker
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# In browser
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# Chrome DevTools → Lighthouse → Accessibility
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# Chrome DevTools → Elements → Accessibility tree
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# Screen reader testing
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# macOS: VoiceOver (Cmd + F5)
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# Windows: NVDA (free) or JAWS
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# Linux: Orca
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```
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## Quick Reference: ARIA Live Regions
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| Value | Behavior | Use For |
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|-------|----------|---------|
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| `aria-live="polite"` | Announced at next pause | Status updates, saved confirmations |
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| `aria-live="assertive"` | Announced immediately | Errors, time-sensitive alerts |
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| `role="status"` | Same as `polite` | Status messages |
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| `role="alert"` | Same as `assertive` | Error messages |
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## Common Anti-Patterns
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| Anti-Pattern | Problem | Fix |
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|---|---|---|
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| `div` as button | Not focusable, no keyboard support | Use `<button>` |
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| Missing `alt` text | Images invisible to screen readers | Add descriptive `alt` |
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| Color-only states | Invisible to color-blind users | Add icons, text, or patterns |
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| Autoplaying media | Disorienting, can't be stopped | Add controls, don't autoplay |
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| Custom dropdown with no ARIA | Unusable by keyboard/screen reader | Use native `<select>` or proper ARIA listbox |
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| Removing focus outlines | Users can't see where they are | Style outlines, don't remove them |
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| Empty links/buttons | "Link" announced with no description | Add text or `aria-label` |
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| `tabindex > 0` | Breaks natural tab order | Use `tabindex="0"` or `-1` only |
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@@ -0,0 +1,370 @@
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# Orchestration Patterns
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Reference catalog of agent orchestration patterns this repo endorses, plus anti-patterns to avoid. Read this before adding a new slash command that coordinates multiple personas, or before introducing a new persona that "wraps" existing ones.
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The governing rule: **the user (or a slash command) is the orchestrator. Personas do not invoke other personas.** Skills are mandatory hops inside a persona's workflow.
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---
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## Endorsed patterns
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### 1. Direct invocation (no orchestration)
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Single persona, single perspective, single artifact. The default and the cheapest option.
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```
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user → code-reviewer → report → user
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```
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**Use when:** the work is one perspective on one artifact and you can describe it in one sentence.
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||||
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||||
**Examples:**
|
||||
- "Review this PR" → `code-reviewer`
|
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- "Find security issues in `auth.ts`" → `security-auditor`
|
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- "What tests are missing for the checkout flow?" → `test-engineer`
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|
||||
**Cost:** one round trip. The baseline you should always compare orchestrated patterns against.
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|
||||
---
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||||
|
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### 2. Single-persona slash command
|
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|
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A slash command that wraps one persona with the project's skills. Saves the user from re-explaining the workflow every time.
|
||||
|
||||
```
|
||||
/review → code-reviewer (with code-review-and-quality skill) → report
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||||
```
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||||
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||||
**Use when:** the same single-persona invocation happens repeatedly with the same setup.
|
||||
|
||||
**Examples in this repo:** `/review`, `/test`, `/code-simplify`.
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||||
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||||
**Cost:** same as direct invocation. The slash command is just a saved prompt.
|
||||
|
||||
**Anti-signal:** if the slash command's body is mostly "decide which persona to call," delete it and let the user call the persona directly.
|
||||
|
||||
---
|
||||
|
||||
### 3. Parallel fan-out with merge
|
||||
|
||||
Multiple personas operate on the same input concurrently, each producing an independent report. A merge step (in the main agent's context) synthesizes them into a single decision.
|
||||
|
||||
```
|
||||
┌─→ code-reviewer ─┐
|
||||
/ship → fan out ───┼─→ security-auditor ─┤→ merge → go/no-go + rollback
|
||||
└─→ test-engineer ─┘
|
||||
```
|
||||
|
||||
**Use when:**
|
||||
- The sub-tasks are genuinely independent (no shared mutable state, no ordering dependency)
|
||||
- Each sub-agent benefits from its own context window
|
||||
- The merge step is small enough to stay in the main context
|
||||
- Wall-clock latency matters
|
||||
|
||||
**Examples in this repo:** `/ship`.
|
||||
|
||||
**Cost:** N parallel sub-agent contexts + one merge turn. Higher than direct invocation, but faster wall-clock and produces better reports because each sub-agent stays focused on its single perspective.
|
||||
|
||||
**Validation checklist before adopting this pattern:**
|
||||
- [ ] Can I run all sub-agents at the same time without ordering issues?
|
||||
- [ ] Does each persona produce a different *kind* of finding, not just the same finding from a different angle?
|
||||
- [ ] Will the merge step fit in the main agent's remaining context?
|
||||
- [ ] Is the user's wait time long enough that parallelism is actually noticeable?
|
||||
|
||||
If any answer is "no," fall back to direct invocation or a single-persona command.
|
||||
|
||||
---
|
||||
|
||||
### 4. Sequential pipeline as user-driven slash commands
|
||||
|
||||
The user runs slash commands in a defined order, carrying context (or commit history) between them. There is no orchestrator agent — the user IS the orchestrator.
|
||||
|
||||
```
|
||||
user runs: /spec → /plan → /build → /test → /review → /ship
|
||||
```
|
||||
|
||||
**Use when:** the workflow has dependencies (each step needs the previous step's output) and human judgment between steps adds value.
|
||||
|
||||
**Examples in this repo:** the entire DEFINE → PLAN → BUILD → VERIFY → REVIEW → SHIP lifecycle.
|
||||
|
||||
**Cost:** one sub-agent context per step. Free for the orchestration layer because there is no orchestrator agent.
|
||||
|
||||
**Why not automate it:** an LLM "lifecycle orchestrator" would (a) lose nuance between steps because it has to summarize for hand-off, (b) skip the human checkpoints that catch wrong-direction work early, and (c) double the token cost via paraphrasing turns.
|
||||
|
||||
---
|
||||
|
||||
### 5. Research isolation (context preservation)
|
||||
|
||||
When a task requires reading large amounts of material that shouldn't pollute the main context, spawn a research sub-agent that returns only a digest.
|
||||
|
||||
```
|
||||
main agent → research sub-agent (reads 50 files) → digest → main agent continues
|
||||
```
|
||||
|
||||
**Use when:**
|
||||
- The main session needs to stay focused on a downstream task
|
||||
- The investigation result is much smaller than the input it consumes
|
||||
- The decision quality benefits from the main agent having room to think after
|
||||
|
||||
**Examples:** "Find every call site of this deprecated API across the monorepo," "Summarize what these 30 ADRs say about caching."
|
||||
|
||||
**Cost:** one isolated sub-agent context. Worth it any time the alternative is loading hundreds of files into the main context.
|
||||
|
||||
**On Claude Code, use the built-in `Explore` subagent** rather than defining a custom research persona. `Explore` runs on Haiku, is denied write/edit tools, and is purpose-built for this pattern. Define a custom research subagent only when `Explore` doesn't fit (e.g. you need a domain-specific system prompt the model wouldn't infer).
|
||||
|
||||
---
|
||||
|
||||
## Claude Code compatibility
|
||||
|
||||
This catalog is harness-agnostic, but most readers will run it on Claude Code. Here's how each pattern maps onto Claude Code's primitives — and where the platform enforces our rules for us.
|
||||
|
||||
### Where personas live
|
||||
|
||||
Plugin subagents go in `agents/` at the plugin root. This repo is a plugin (`.claude-plugin/plugin.json`), so `agents/code-reviewer.md`, `agents/security-auditor.md`, and `agents/test-engineer.md` are auto-discovered when the plugin is enabled. No path configuration needed.
|
||||
|
||||
### Subagents vs. Agent Teams
|
||||
|
||||
Claude Code has two parallelism primitives. Pattern 3 (parallel fan-out with merge) maps to **subagents**. If you need teammates that talk to each other, use **Agent Teams** instead.
|
||||
|
||||
| | Subagents | Agent Teams |
|
||||
|--|-----------|-------------|
|
||||
| Coordination | Main agent fans out, sub-agents only report back | Teammates message each other, share a task list |
|
||||
| Context | Own context window per subagent | Own context window per teammate |
|
||||
| When to use | Independent tasks producing reports | Collaborative work needing discussion |
|
||||
| Status | Stable | Experimental — requires `CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1` |
|
||||
| Cost | Lower | Higher — each teammate is a separate Claude instance |
|
||||
|
||||
**The personas in this repo work in both modes.** When spawned as subagents (e.g. by `/ship`), they report findings to the main session. When spawned as teammates (`Spawn a teammate using the security-auditor agent type…`), they can challenge each other's findings directly. The persona definition is the same; only the spawning context changes.
|
||||
|
||||
One subtlety: the `skills` and `mcpServers` frontmatter fields in a persona are honored when it runs as a subagent but **ignored when it runs as a teammate** — teammates load skills and MCP servers from your project and user settings, the same as a regular session. If a persona depends on a specific skill or MCP server being loaded, configure it at the session level so it's available in both modes.
|
||||
|
||||
### Platform-enforced rules
|
||||
|
||||
Two rules in this catalog aren't just convention — Claude Code enforces them:
|
||||
|
||||
- **"Subagents cannot spawn other subagents"** (verbatim from the docs). Anti-pattern B (persona-calls-persona) and Anti-pattern D (deep persona trees) cannot exist on Claude Code by construction.
|
||||
- **"No nested teams"** — teammates cannot spawn their own teams. Same anti-patterns blocked at the team level.
|
||||
|
||||
This means you can adopt the patterns in this catalog without worrying about contributors accidentally building the anti-patterns. They'll just fail to load.
|
||||
|
||||
### Built-in subagents to know about
|
||||
|
||||
Before defining a custom subagent, check whether one of these covers the role:
|
||||
|
||||
| Built-in | Purpose |
|
||||
|----------|---------|
|
||||
| `Explore` | Read-only codebase search and analysis. Use this for Pattern 5 (research isolation). |
|
||||
| `Plan` | Read-only research during plan mode. |
|
||||
| `general-purpose` | Multi-step tasks needing both exploration and modification. |
|
||||
|
||||
Don't redefine these. Layer your specialist personas (code-reviewer, security-auditor, test-engineer) on top of them.
|
||||
|
||||
### Frontmatter restrictions for plugin agents
|
||||
|
||||
Plugin subagents do **not** support the `hooks`, `mcpServers`, or `permissionMode` frontmatter fields — these are silently ignored. If a future persona needs any of those, the user must copy the file into `.claude/agents/` or `~/.claude/agents/` instead.
|
||||
|
||||
The fields that DO work in plugin agents are: `name`, `description`, `tools`, `disallowedTools`, `model`, `maxTurns`, `skills`, `memory`, `background`, `effort`, `isolation`, `color`, `initialPrompt`. Use `model` per-persona if you want to optimize cost (e.g. Haiku for `test-engineer` coverage scans, Sonnet for `code-reviewer`, Opus for `security-auditor`).
|
||||
|
||||
### Spawning multiple subagents in parallel
|
||||
|
||||
In Claude Code, parallel fan-out (Pattern 3) requires issuing **multiple Agent tool calls in a single assistant turn**. Sequential turns serialize execution. `/ship` calls this out explicitly. Any new orchestrator command should do the same.
|
||||
|
||||
---
|
||||
|
||||
## Worked example: Agent Teams for competing-hypothesis debugging
|
||||
|
||||
This example shows when to reach for **Agent Teams** instead of `/ship`'s subagent fan-out. The two patterns look similar from a distance — both spawn the same three personas — but the value comes from a different place.
|
||||
|
||||
### The scenario
|
||||
|
||||
> *Checkout occasionally hangs for ~30 seconds before completing. It happens roughly once every 50 sessions. No errors in logs. Started after last week's release.*
|
||||
|
||||
Plausible root causes (mutually exclusive, all fit the symptoms):
|
||||
|
||||
1. A race condition in the new payment-confirmation flow
|
||||
2. An auth check that occasionally falls through to a slow synchronous network call
|
||||
3. A missing index on a query that scales with cart size
|
||||
4. A flaky third-party API where the SDK retries silently before timing out
|
||||
|
||||
A single agent will pick the first plausible theory and stop investigating. A `/ship`-style subagent fan-out would have each persona report independently — but their reports never meet, so nothing rules out the wrong theories.
|
||||
|
||||
This is exactly the case the Agent Teams docs describe: *"With multiple independent investigators actively trying to disprove each other, the theory that survives is much more likely to be the actual root cause."*
|
||||
|
||||
### Why this is *not* a `/ship` job
|
||||
|
||||
| | `/ship` (subagents) | Agent Teams |
|
||||
|--|--------------------|-------------|
|
||||
| Sub-agents see | The same diff, different lenses | A shared task list, each other's messages |
|
||||
| Output | Three independent reports → one merge | Adversarial debate → consensus root cause |
|
||||
| Right when | You want a verdict on a known artifact | You want to *find* the artifact among hypotheses |
|
||||
|
||||
`/ship` is a verdict; Agent Teams is an investigation.
|
||||
|
||||
### Setup (one-time, per-environment)
|
||||
|
||||
Agent Teams is experimental. In `~/.claude/settings.json`:
|
||||
|
||||
```json
|
||||
{
|
||||
"env": {
|
||||
"CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS": "1"
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
Requires Claude Code v2.1.32 or later. The personas in this repo are picked up automatically — no team-config files to author by hand.
|
||||
|
||||
### The trigger prompt
|
||||
|
||||
Type into the lead session, in natural language:
|
||||
|
||||
```
|
||||
Users report checkout hangs for ~30 seconds intermittently after last
|
||||
week's release. No errors in logs.
|
||||
|
||||
Create an agent team to debug this with competing hypotheses. Spawn
|
||||
three teammates using the existing agent types:
|
||||
|
||||
- code-reviewer — investigate race conditions and blocking calls
|
||||
in the checkout code path
|
||||
- security-auditor — investigate auth checks, session handling,
|
||||
and any synchronous network calls added recently
|
||||
- test-engineer — propose tests that would distinguish between the
|
||||
hypotheses and check coverage gaps in checkout
|
||||
|
||||
Have them message each other directly to challenge each other's
|
||||
theories. Update findings as consensus emerges. Only converge when
|
||||
two teammates agree they can disprove the others'.
|
||||
```
|
||||
|
||||
The lead spawns three teammates referencing the existing persona names. The persona body is **appended** to each teammate's system prompt as additional instructions (on top of the team-coordination instructions the lead installs); the trigger prompt above becomes their task.
|
||||
|
||||
### What happens
|
||||
|
||||
1. Each teammate runs in its own context window, exploring the codebase from its own lens.
|
||||
2. Teammates use `message` to send findings to each other directly. The lead doesn't have to relay.
|
||||
3. The shared task list shows who's investigating what — visible at any time with `Ctrl+T` (in-process mode) or in a tmux pane (split mode).
|
||||
4. When `code-reviewer` finds a `Promise.all` that should be sequential, it messages `security-auditor` to confirm the auth call isn't part of the race. `security-auditor` checks and replies — either confirming the race is the real issue or producing counter-evidence.
|
||||
5. `test-engineer` proposes a focused integration test for whichever theory is winning, which the team uses to verify before declaring consensus.
|
||||
6. The lead synthesizes the converged finding and presents it to you.
|
||||
|
||||
You can interrupt at any teammate by cycling with `Shift+Down` and typing — useful for redirecting an investigator who's gone down a wrong path.
|
||||
|
||||
### When to clean up
|
||||
|
||||
When the investigation lands on a root cause, tell the lead:
|
||||
|
||||
```
|
||||
Clean up the team
|
||||
```
|
||||
|
||||
Always cleanup through the lead, not a teammate (per the docs: teammates lack full team context for cleanup).
|
||||
|
||||
### Cost expectation
|
||||
|
||||
Three Sonnet teammates running for ~10–15 minutes of investigation costs noticeably more than the same three personas spawned as subagents by `/ship`. The justification is *quality of conclusion* — for production debugging where the wrong fix is expensive, the extra tokens are a bargain. For a routine PR review, stick with `/ship`.
|
||||
|
||||
### Anti-pattern in this scenario
|
||||
|
||||
Do **not** rebuild this as a `/debug` slash command that fans out subagents. Subagents can't message each other — you'd lose the adversarial debate that makes the pattern work. If a workflow keeps coming up, document the trigger prompt above as a snippet rather than wrapping it in a slash command that misuses subagents.
|
||||
|
||||
### When *not* to use Agent Teams
|
||||
|
||||
- Production-bound verdict on a known diff → use `/ship` (subagents).
|
||||
- One specialist perspective on one artifact → direct persona invocation.
|
||||
- Sequential lifecycle (spec → plan → build) → user-driven slash commands (Pattern 4).
|
||||
- Read-heavy research with a small digest → built-in `Explore` subagent.
|
||||
|
||||
Reach for Agent Teams only when teammates **need** to challenge each other to produce the right answer.
|
||||
|
||||
---
|
||||
|
||||
## Anti-patterns
|
||||
|
||||
### A. Router persona ("meta-orchestrator")
|
||||
|
||||
A persona whose job is to decide which other persona to call.
|
||||
|
||||
```
|
||||
/work → router-persona → "this needs a review" → code-reviewer → router (paraphrases) → user
|
||||
```
|
||||
|
||||
**Why it fails:**
|
||||
- Pure routing layer with no domain value
|
||||
- Adds two paraphrasing hops → information loss + roughly 2× token cost
|
||||
- The user already knew they wanted a review; they could have called `/review` directly
|
||||
- Replicates the work that slash commands and intent mapping in `AGENTS.md` already do
|
||||
|
||||
**What to do instead:** add or refine slash commands. Document intent → command mapping in `AGENTS.md`.
|
||||
|
||||
---
|
||||
|
||||
### B. Persona that calls another persona
|
||||
|
||||
A `code-reviewer` that internally invokes `security-auditor` when it sees auth code.
|
||||
|
||||
**Why it fails:**
|
||||
- Personas were designed to produce a single perspective; chaining them defeats that
|
||||
- The summary the calling persona passes loses context the called persona needs
|
||||
- Failure modes multiply (which persona's output format wins? whose rules apply?)
|
||||
- Hides cost from the user
|
||||
|
||||
**What to do instead:** have the calling persona *recommend* a follow-up audit in its report. The user or a slash command runs the second pass.
|
||||
|
||||
---
|
||||
|
||||
### C. Sequential orchestrator that paraphrases
|
||||
|
||||
An agent that calls `/spec`, then `/plan`, then `/build`, etc. on the user's behalf.
|
||||
|
||||
**Why it fails:**
|
||||
- Loses the human checkpoints that catch wrong-direction work
|
||||
- Each hand-off summarizes context — accumulated drift over a long pipeline
|
||||
- Doubles token cost: orchestrator turn + sub-agent turn for every step
|
||||
- Removes user agency at exactly the points where judgment matters most
|
||||
|
||||
**What to do instead:** keep the user as the orchestrator. Document the recommended sequence in `README.md` and let users invoke it.
|
||||
|
||||
---
|
||||
|
||||
### D. Deep persona trees
|
||||
|
||||
`/ship` calls a `pre-ship-coordinator` that calls a `quality-coordinator` that calls `code-reviewer`.
|
||||
|
||||
**Why it fails:**
|
||||
- Each layer adds latency and tokens with no decision value
|
||||
- Debugging becomes a multi-level investigation
|
||||
- The leaf personas lose context to multiple summarization steps
|
||||
|
||||
**What to do instead:** keep the orchestration depth at most 1 (slash command → personas). The merge happens in the main agent.
|
||||
|
||||
---
|
||||
|
||||
## Decision flow
|
||||
|
||||
When considering a new orchestrated workflow, walk this flow:
|
||||
|
||||
```
|
||||
Is the work one perspective on one artifact?
|
||||
├── Yes → Direct invocation. Stop.
|
||||
└── No → Will the same composition repeat?
|
||||
├── No → Direct invocation, ad hoc. Stop.
|
||||
└── Yes → Are sub-tasks independent?
|
||||
├── No → Sequential slash commands run by user (Pattern 4).
|
||||
└── Yes → Parallel fan-out with merge (Pattern 3).
|
||||
Validate against the checklist above.
|
||||
If any check fails → fall back to single-persona command (Pattern 2).
|
||||
```
|
||||
|
||||
---
|
||||
|
||||
## When to add a new pattern to this catalog
|
||||
|
||||
Add a new entry only after:
|
||||
|
||||
1. You've used the pattern at least twice in real work
|
||||
2. You can name a concrete artifact in this repo that demonstrates it
|
||||
3. You can explain why an existing pattern wouldn't have worked
|
||||
4. You can describe its anti-pattern shadow (what people will mistakenly build instead)
|
||||
|
||||
Premature catalog entries become aspirational documentation that no one follows.
|
||||
@@ -0,0 +1,153 @@
|
||||
# Performance Checklist
|
||||
|
||||
Quick reference checklist for web application performance. Use alongside the `performance-optimization` skill.
|
||||
|
||||
## Table of Contents
|
||||
|
||||
- [Core Web Vitals Targets](#core-web-vitals-targets)
|
||||
- [TTFB Diagnosis](#ttfb-diagnosis)
|
||||
- [Frontend Checklist](#frontend-checklist)
|
||||
- [Backend Checklist](#backend-checklist)
|
||||
- [Measurement Commands](#measurement-commands)
|
||||
- [Common Anti-Patterns](#common-anti-patterns)
|
||||
|
||||
## Core Web Vitals Targets
|
||||
|
||||
| Metric | Good | Needs Work | Poor |
|
||||
|--------|------|------------|------|
|
||||
| LCP (Largest Contentful Paint) | ≤ 2.5s | ≤ 4.0s | > 4.0s |
|
||||
| INP (Interaction to Next Paint) | ≤ 200ms | ≤ 500ms | > 500ms |
|
||||
| CLS (Cumulative Layout Shift) | ≤ 0.1 | ≤ 0.25 | > 0.25 |
|
||||
|
||||
## TTFB Diagnosis
|
||||
|
||||
When TTFB is slow (> 800ms), check each component in DevTools Network waterfall:
|
||||
|
||||
- [ ] **DNS resolution** slow → add `<link rel="dns-prefetch">` or `<link rel="preconnect">` for known origins
|
||||
- [ ] **TCP/TLS handshake** slow → enable HTTP/2, consider edge deployment, verify keep-alive
|
||||
- [ ] **Server processing** slow → profile backend, check slow queries, add caching
|
||||
|
||||
## Frontend Checklist
|
||||
|
||||
### Images
|
||||
- [ ] Images use modern formats (WebP, AVIF)
|
||||
- [ ] Images are responsively sized (`srcset` and `sizes`)
|
||||
- [ ] Images and `<source>` elements have explicit `width` and `height` (prevents CLS in art direction)
|
||||
- [ ] Below-the-fold images use `loading="lazy"` and `decoding="async"`
|
||||
- [ ] Hero/LCP images use `fetchpriority="high"` and no lazy loading
|
||||
|
||||
### JavaScript
|
||||
- [ ] Bundle size under 200KB gzipped (initial load)
|
||||
- [ ] Code splitting with dynamic `import()` for routes and heavy features
|
||||
- [ ] Tree shaking enabled (verify dependency ships ESM and marks `sideEffects: false`)
|
||||
- [ ] No blocking JavaScript in `<head>` (use `defer` or `async`)
|
||||
- [ ] Heavy computation offloaded to Web Workers (if applicable)
|
||||
- [ ] `React.memo()` on expensive components that re-render with same props
|
||||
- [ ] `useMemo()` / `useCallback()` only where profiling shows benefit
|
||||
- [ ] Long tasks (> 50ms) broken up to keep the main thread available — main lever for INP
|
||||
- [ ] `yieldToMain` pattern used inside long-running loops so input events can run between chunks
|
||||
- [ ] Modern scheduling APIs used where available: `scheduler.yield()` (preferred), `scheduler.postTask()` with priorities, `isInputPending()` to yield only when needed
|
||||
- [ ] `requestIdleCallback` for deferrable, non-urgent work (analytics flush, prefetch, warmup)
|
||||
- [ ] Non-critical work deferred out of event handlers (e.g. analytics, logging) so the response to the interaction is not delayed
|
||||
- [ ] Third-party scripts loaded with `async` / `defer`, audited for size, and fronted by a facade when heavy (chat widgets, embeds)
|
||||
|
||||
### CSS
|
||||
- [ ] Critical CSS inlined or preloaded
|
||||
- [ ] No render-blocking CSS for non-critical styles
|
||||
- [ ] No CSS-in-JS runtime cost in production (use extraction)
|
||||
|
||||
### Fonts
|
||||
- [ ] Limited to 2–3 font families, 2–3 weights each (every additional weight is another request)
|
||||
- [ ] WOFF2 format only (smallest, universal support — skip WOFF/TTF/EOT)
|
||||
- [ ] Self-hosted when possible (third-party font CDNs add DNS + TCP + TLS round-trips)
|
||||
- [ ] LCP-critical fonts preloaded: `<link rel="preload" as="font" type="font/woff2" crossorigin>`
|
||||
- [ ] `font-display: swap` (or `optional` for non-critical) to avoid FOIT blocking render
|
||||
- [ ] Subsetted via `unicode-range` to ship only the glyphs each page needs
|
||||
- [ ] Variable fonts considered when multiple weights/styles are required (one file replaces many)
|
||||
- [ ] Fallback font metrics adjusted with `size-adjust`, `ascent-override`, `descent-override` to reduce CLS on font swap
|
||||
- [ ] System font stack considered before any custom font
|
||||
|
||||
### Network
|
||||
- [ ] Static assets cached with long `max-age` + content hashing
|
||||
- [ ] API responses cached where appropriate (`Cache-Control`)
|
||||
- [ ] HTTP/2 or HTTP/3 enabled
|
||||
- [ ] Resources preconnected (`<link rel="preconnect">`) for known origins
|
||||
- [ ] `fetchpriority` used on critical non-image resources (e.g., key `<link rel="preload">`, above-the-fold `<script>`) — not only on `<img>`
|
||||
- [ ] No unnecessary redirects
|
||||
|
||||
### Rendering
|
||||
- [ ] No layout thrashing (forced synchronous layouts)
|
||||
- [ ] Animations use `transform` and `opacity` (GPU-accelerated)
|
||||
- [ ] Long lists use virtualization (e.g., `react-window`)
|
||||
- [ ] No unnecessary full-page re-renders
|
||||
- [ ] Off-screen sections use `content-visibility: auto` with `contain-intrinsic-size` to skip layout/paint of non-visible areas
|
||||
- [ ] No `unload` event handlers and no `Cache-Control: no-store` on HTML responses — preserves back/forward cache (bfcache) eligibility
|
||||
|
||||
## Backend Checklist
|
||||
|
||||
### Database
|
||||
- [ ] No N+1 query patterns (use eager loading / joins)
|
||||
- [ ] Queries have appropriate indexes
|
||||
- [ ] List endpoints paginated (never `SELECT * FROM table`)
|
||||
- [ ] Connection pooling configured
|
||||
- [ ] Slow query logging enabled
|
||||
|
||||
### API
|
||||
- [ ] Response times < 200ms (p95)
|
||||
- [ ] No synchronous heavy computation in request handlers
|
||||
- [ ] Bulk operations instead of loops of individual calls
|
||||
- [ ] Response compression (gzip/brotli)
|
||||
- [ ] Appropriate caching (in-memory, Redis, CDN)
|
||||
|
||||
### Infrastructure
|
||||
- [ ] CDN for static assets
|
||||
- [ ] Server located close to users (or edge deployment)
|
||||
- [ ] Horizontal scaling configured (if needed)
|
||||
- [ ] Health check endpoint for load balancer
|
||||
|
||||
## Measurement Commands
|
||||
|
||||
### INP field data and DevTools workflow
|
||||
|
||||
1. **Field data first** — check [CrUX Vis](https://developer.chrome.com/docs/crux/vis) or your RUM tool for real-user INP before optimising
|
||||
2. **Identify slow interactions** — open DevTools → Performance panel → record while interacting; look for long tasks triggered by clicks/keystrokes
|
||||
3. **Test on mid-range Android** — INP issues often only surface on slower hardware; use a real device or DevTools CPU throttling (4×–6× slowdown)
|
||||
|
||||
```bash
|
||||
# Lighthouse CLI
|
||||
npx lighthouse https://localhost:3000 --output json --output-path ./report.json
|
||||
|
||||
# Bundle analysis
|
||||
npx webpack-bundle-analyzer stats.json
|
||||
# or for Vite:
|
||||
npx vite-bundle-visualizer
|
||||
|
||||
# Check bundle size
|
||||
npx bundlesize
|
||||
|
||||
# Web Vitals in code
|
||||
import { onLCP, onINP, onCLS } from 'web-vitals';
|
||||
onLCP(console.log);
|
||||
onINP(console.log);
|
||||
onCLS(console.log);
|
||||
|
||||
# INP with interaction-level detail (attribution build)
|
||||
import { onINP } from 'web-vitals/attribution';
|
||||
onINP(({ value, attribution }) => {
|
||||
const { interactionTarget, inputDelay, processingDuration, presentationDelay } = attribution;
|
||||
console.log({ value, interactionTarget, inputDelay, processingDuration, presentationDelay });
|
||||
});
|
||||
```
|
||||
|
||||
## Common Anti-Patterns
|
||||
|
||||
| Anti-Pattern | Impact | Fix |
|
||||
|---|---|---|
|
||||
| N+1 queries | Linear DB load growth | Use joins, includes, or batch loading |
|
||||
| Unbounded queries | Memory exhaustion, timeouts | Always paginate, add LIMIT |
|
||||
| Missing indexes | Slow reads as data grows | Add indexes for filtered/sorted columns |
|
||||
| Layout thrashing | Jank, dropped frames | Batch DOM reads, then batch writes |
|
||||
| Unoptimized images | Slow LCP, wasted bandwidth | Use WebP, responsive sizes, lazy load |
|
||||
| Large bundles | Slow Time to Interactive | Code split, tree shake, audit deps |
|
||||
| Blocking main thread | Poor INP, unresponsive UI | Chunk long tasks with `scheduler.yield()` / `yieldToMain`, offload to Web Workers |
|
||||
| Memory leaks | Growing memory, eventual crash | Clean up listeners, intervals, refs |
|
||||
@@ -0,0 +1,134 @@
|
||||
# Security Checklist
|
||||
|
||||
Quick reference for web application security. Use alongside the `security-and-hardening` skill.
|
||||
|
||||
## Table of Contents
|
||||
|
||||
- [Pre-Commit Checks](#pre-commit-checks)
|
||||
- [Authentication](#authentication)
|
||||
- [Authorization](#authorization)
|
||||
- [Input Validation](#input-validation)
|
||||
- [Security Headers](#security-headers)
|
||||
- [CORS Configuration](#cors-configuration)
|
||||
- [Data Protection](#data-protection)
|
||||
- [Dependency Security](#dependency-security)
|
||||
- [Error Handling](#error-handling)
|
||||
- [OWASP Top 10 Quick Reference](#owasp-top-10-quick-reference)
|
||||
|
||||
## Pre-Commit Checks
|
||||
|
||||
- [ ] No secrets in code (`git diff --cached | grep -i "password\|secret\|api_key\|token"`)
|
||||
- [ ] `.gitignore` covers: `.env`, `.env.local`, `*.pem`, `*.key`
|
||||
- [ ] `.env.example` uses placeholder values (not real secrets)
|
||||
|
||||
## Authentication
|
||||
|
||||
- [ ] Passwords hashed with bcrypt (≥12 rounds), scrypt, or argon2
|
||||
- [ ] Session cookies: `httpOnly`, `secure`, `sameSite: 'lax'`
|
||||
- [ ] Session expiration configured (reasonable max-age)
|
||||
- [ ] Rate limiting on login endpoint (≤10 attempts per 15 minutes)
|
||||
- [ ] Password reset tokens: time-limited (≤1 hour), single-use
|
||||
- [ ] Account lockout after repeated failures (optional, with notification)
|
||||
- [ ] MFA supported for sensitive operations (optional but recommended)
|
||||
|
||||
## Authorization
|
||||
|
||||
- [ ] Every protected endpoint checks authentication
|
||||
- [ ] Every resource access checks ownership/role (prevents IDOR)
|
||||
- [ ] Admin endpoints require admin role verification
|
||||
- [ ] API keys scoped to minimum necessary permissions
|
||||
- [ ] JWT tokens validated (signature, expiration, issuer)
|
||||
|
||||
## Input Validation
|
||||
|
||||
- [ ] All user input validated at system boundaries (API routes, form handlers)
|
||||
- [ ] Validation uses allowlists (not denylists)
|
||||
- [ ] String lengths constrained (min/max)
|
||||
- [ ] Numeric ranges validated
|
||||
- [ ] Email, URL, and date formats validated with proper libraries
|
||||
- [ ] File uploads: type restricted, size limited, content verified
|
||||
- [ ] SQL queries parameterized (no string concatenation)
|
||||
- [ ] HTML output encoded (use framework auto-escaping)
|
||||
- [ ] URLs validated before redirect (prevent open redirect)
|
||||
|
||||
## Security Headers
|
||||
|
||||
```
|
||||
Content-Security-Policy: default-src 'self'; script-src 'self'
|
||||
Strict-Transport-Security: max-age=31536000; includeSubDomains
|
||||
X-Content-Type-Options: nosniff
|
||||
X-Frame-Options: DENY
|
||||
X-XSS-Protection: 0 (disabled, rely on CSP)
|
||||
Referrer-Policy: strict-origin-when-cross-origin
|
||||
Permissions-Policy: camera=(), microphone=(), geolocation=()
|
||||
```
|
||||
|
||||
## CORS Configuration
|
||||
|
||||
```typescript
|
||||
// Restrictive (recommended)
|
||||
cors({
|
||||
origin: ['https://yourdomain.com', 'https://app.yourdomain.com'],
|
||||
credentials: true,
|
||||
methods: ['GET', 'POST', 'PUT', 'PATCH', 'DELETE'],
|
||||
allowedHeaders: ['Content-Type', 'Authorization'],
|
||||
})
|
||||
|
||||
// NEVER use in production:
|
||||
cors({ origin: '*' }) // Allows any origin
|
||||
```
|
||||
|
||||
## Data Protection
|
||||
|
||||
- [ ] Sensitive fields excluded from API responses (`passwordHash`, `resetToken`, etc.)
|
||||
- [ ] Sensitive data not logged (passwords, tokens, full CC numbers)
|
||||
- [ ] PII encrypted at rest (if required by regulation)
|
||||
- [ ] HTTPS for all external communication
|
||||
- [ ] Database backups encrypted
|
||||
|
||||
## Dependency Security
|
||||
|
||||
```bash
|
||||
# Audit dependencies
|
||||
npm audit
|
||||
|
||||
# Fix automatically where possible
|
||||
npm audit fix
|
||||
|
||||
# Check for critical vulnerabilities
|
||||
npm audit --audit-level=critical
|
||||
|
||||
# Keep dependencies updated
|
||||
npx npm-check-updates
|
||||
```
|
||||
|
||||
## Error Handling
|
||||
|
||||
```typescript
|
||||
// Production: generic error, no internals
|
||||
res.status(500).json({
|
||||
error: { code: 'INTERNAL_ERROR', message: 'Something went wrong' }
|
||||
});
|
||||
|
||||
// NEVER in production:
|
||||
res.status(500).json({
|
||||
error: err.message,
|
||||
stack: err.stack, // Exposes internals
|
||||
query: err.sql, // Exposes database details
|
||||
});
|
||||
```
|
||||
|
||||
## OWASP Top 10 Quick Reference
|
||||
|
||||
| # | Vulnerability | Prevention |
|
||||
|---|---|---|
|
||||
| 1 | Broken Access Control | Auth checks on every endpoint, ownership verification |
|
||||
| 2 | Cryptographic Failures | HTTPS, strong hashing, no secrets in code |
|
||||
| 3 | Injection | Parameterized queries, input validation |
|
||||
| 4 | Insecure Design | Threat modeling, spec-driven development |
|
||||
| 5 | Security Misconfiguration | Security headers, minimal permissions, audit deps |
|
||||
| 6 | Vulnerable Components | `npm audit`, keep deps updated, minimal deps |
|
||||
| 7 | Auth Failures | Strong passwords, rate limiting, session management |
|
||||
| 8 | Data Integrity Failures | Verify updates/dependencies, signed artifacts |
|
||||
| 9 | Logging Failures | Log security events, don't log secrets |
|
||||
| 10 | SSRF | Validate/allowlist URLs, restrict outbound requests |
|
||||
@@ -0,0 +1,236 @@
|
||||
# Testing Patterns Reference
|
||||
|
||||
Quick reference for common testing patterns across the stack. Use alongside the `test-driven-development` skill.
|
||||
|
||||
## Table of Contents
|
||||
|
||||
- [Test Structure (Arrange-Act-Assert)](#test-structure-arrange-act-assert)
|
||||
- [Test Naming Conventions](#test-naming-conventions)
|
||||
- [Common Assertions](#common-assertions)
|
||||
- [Mocking Patterns](#mocking-patterns)
|
||||
- [React/Component Testing](#reactcomponent-testing)
|
||||
- [API / Integration Testing](#api--integration-testing)
|
||||
- [E2E Testing (Playwright)](#e2e-testing-playwright)
|
||||
- [Test Anti-Patterns](#test-anti-patterns)
|
||||
|
||||
## Test Structure (Arrange-Act-Assert)
|
||||
|
||||
```typescript
|
||||
it('describes expected behavior', () => {
|
||||
// Arrange: Set up test data and preconditions
|
||||
const input = { title: 'Test Task', priority: 'high' };
|
||||
|
||||
// Act: Perform the action being tested
|
||||
const result = createTask(input);
|
||||
|
||||
// Assert: Verify the outcome
|
||||
expect(result.title).toBe('Test Task');
|
||||
expect(result.priority).toBe('high');
|
||||
expect(result.status).toBe('pending');
|
||||
});
|
||||
```
|
||||
|
||||
## Test Naming Conventions
|
||||
|
||||
```typescript
|
||||
// Pattern: [unit] [expected behavior] [condition]
|
||||
describe('TaskService.createTask', () => {
|
||||
it('creates a task with default pending status', () => {});
|
||||
it('throws ValidationError when title is empty', () => {});
|
||||
it('trims whitespace from title', () => {});
|
||||
it('generates a unique ID for each task', () => {});
|
||||
});
|
||||
```
|
||||
|
||||
## Common Assertions
|
||||
|
||||
```typescript
|
||||
// Equality
|
||||
expect(result).toBe(expected); // Strict equality (===)
|
||||
expect(result).toEqual(expected); // Deep equality (objects/arrays)
|
||||
expect(result).toStrictEqual(expected); // Deep equality + type matching
|
||||
|
||||
// Truthiness
|
||||
expect(result).toBeTruthy();
|
||||
expect(result).toBeFalsy();
|
||||
expect(result).toBeNull();
|
||||
expect(result).toBeDefined();
|
||||
expect(result).toBeUndefined();
|
||||
|
||||
// Numbers
|
||||
expect(result).toBeGreaterThan(5);
|
||||
expect(result).toBeLessThanOrEqual(10);
|
||||
expect(result).toBeCloseTo(0.3, 5); // Floating point
|
||||
|
||||
// Strings
|
||||
expect(result).toMatch(/pattern/);
|
||||
expect(result).toContain('substring');
|
||||
|
||||
// Arrays / Objects
|
||||
expect(array).toContain(item);
|
||||
expect(array).toHaveLength(3);
|
||||
expect(object).toHaveProperty('key', 'value');
|
||||
|
||||
// Errors
|
||||
expect(() => fn()).toThrow();
|
||||
expect(() => fn()).toThrow(ValidationError);
|
||||
expect(() => fn()).toThrow('specific message');
|
||||
|
||||
// Async
|
||||
await expect(asyncFn()).resolves.toBe(value);
|
||||
await expect(asyncFn()).rejects.toThrow(Error);
|
||||
```
|
||||
|
||||
## Mocking Patterns
|
||||
|
||||
### Mock Functions
|
||||
|
||||
```typescript
|
||||
const mockFn = jest.fn();
|
||||
mockFn.mockReturnValue(42);
|
||||
mockFn.mockResolvedValue({ data: 'test' });
|
||||
mockFn.mockImplementation((x) => x * 2);
|
||||
|
||||
expect(mockFn).toHaveBeenCalled();
|
||||
expect(mockFn).toHaveBeenCalledWith('arg1', 'arg2');
|
||||
expect(mockFn).toHaveBeenCalledTimes(3);
|
||||
```
|
||||
|
||||
### Mock Modules
|
||||
|
||||
```typescript
|
||||
// Mock an entire module
|
||||
jest.mock('./database', () => ({
|
||||
query: jest.fn().mockResolvedValue([{ id: 1, title: 'Test' }]),
|
||||
}));
|
||||
|
||||
// Mock specific exports
|
||||
jest.mock('./utils', () => ({
|
||||
...jest.requireActual('./utils'),
|
||||
generateId: jest.fn().mockReturnValue('test-id'),
|
||||
}));
|
||||
```
|
||||
|
||||
### Mock at Boundaries Only
|
||||
|
||||
```
|
||||
Mock these: Don't mock these:
|
||||
├── Database calls ├── Internal utility functions
|
||||
├── HTTP requests ├── Business logic
|
||||
├── File system operations ├── Data transformations
|
||||
├── External API calls ├── Validation functions
|
||||
└── Time/Date (when needed) └── Pure functions
|
||||
```
|
||||
|
||||
## React/Component Testing
|
||||
|
||||
```tsx
|
||||
import { render, screen, fireEvent, waitFor } from '@testing-library/react';
|
||||
|
||||
describe('TaskForm', () => {
|
||||
it('submits the form with entered data', async () => {
|
||||
const onSubmit = jest.fn();
|
||||
render(<TaskForm onSubmit={onSubmit} />);
|
||||
|
||||
// Find elements by accessible role/label (not test IDs)
|
||||
await screen.findByRole('textbox', { name: /title/i });
|
||||
fireEvent.change(screen.getByRole('textbox', { name: /title/i }), {
|
||||
target: { value: 'New Task' },
|
||||
});
|
||||
fireEvent.click(screen.getByRole('button', { name: /create/i }));
|
||||
|
||||
await waitFor(() => {
|
||||
expect(onSubmit).toHaveBeenCalledWith({ title: 'New Task' });
|
||||
});
|
||||
});
|
||||
|
||||
it('shows validation error for empty title', async () => {
|
||||
render(<TaskForm onSubmit={jest.fn()} />);
|
||||
|
||||
fireEvent.click(screen.getByRole('button', { name: /create/i }));
|
||||
|
||||
expect(await screen.findByText(/title is required/i)).toBeInTheDocument();
|
||||
});
|
||||
});
|
||||
```
|
||||
|
||||
## API / Integration Testing
|
||||
|
||||
```typescript
|
||||
import request from 'supertest';
|
||||
import { app } from '../src/app';
|
||||
|
||||
describe('POST /api/tasks', () => {
|
||||
it('creates a task and returns 201', async () => {
|
||||
const response = await request(app)
|
||||
.post('/api/tasks')
|
||||
.send({ title: 'Test Task' })
|
||||
.set('Authorization', `Bearer ${testToken}`)
|
||||
.expect(201);
|
||||
|
||||
expect(response.body).toMatchObject({
|
||||
id: expect.any(String),
|
||||
title: 'Test Task',
|
||||
status: 'pending',
|
||||
});
|
||||
});
|
||||
|
||||
it('returns 422 for invalid input', async () => {
|
||||
const response = await request(app)
|
||||
.post('/api/tasks')
|
||||
.send({ title: '' })
|
||||
.set('Authorization', `Bearer ${testToken}`)
|
||||
.expect(422);
|
||||
|
||||
expect(response.body.error.code).toBe('VALIDATION_ERROR');
|
||||
});
|
||||
|
||||
it('returns 401 without authentication', async () => {
|
||||
await request(app)
|
||||
.post('/api/tasks')
|
||||
.send({ title: 'Test' })
|
||||
.expect(401);
|
||||
});
|
||||
});
|
||||
```
|
||||
|
||||
## E2E Testing (Playwright)
|
||||
|
||||
```typescript
|
||||
import { test, expect } from '@playwright/test';
|
||||
|
||||
test('user can create and complete a task', async ({ page }) => {
|
||||
// Navigate and authenticate
|
||||
await page.goto('/');
|
||||
await page.fill('[name="email"]', 'test@example.com');
|
||||
await page.fill('[name="password"]', 'testpass123');
|
||||
await page.click('button:has-text("Log in")');
|
||||
|
||||
// Create a task
|
||||
await page.click('button:has-text("New Task")');
|
||||
await page.fill('[name="title"]', 'Buy groceries');
|
||||
await page.click('button:has-text("Create")');
|
||||
|
||||
// Verify task appears
|
||||
await expect(page.locator('text=Buy groceries')).toBeVisible();
|
||||
|
||||
// Complete the task
|
||||
await page.click('[aria-label="Complete Buy groceries"]');
|
||||
await expect(page.locator('text=Buy groceries')).toHaveCSS(
|
||||
'text-decoration-line', 'line-through'
|
||||
);
|
||||
});
|
||||
```
|
||||
|
||||
## Test Anti-Patterns
|
||||
|
||||
| Anti-Pattern | Problem | Better Approach |
|
||||
|---|---|---|
|
||||
| Testing implementation details | Breaks on refactor | Test inputs/outputs |
|
||||
| Snapshot everything | No one reviews snapshot diffs | Assert specific values |
|
||||
| Shared mutable state | Tests pollute each other | Setup/teardown per test |
|
||||
| Testing third-party code | Wastes time, not your bug | Mock the boundary |
|
||||
| Skipping tests to pass CI | Hides real bugs | Fix or delete the test |
|
||||
| Using `test.skip` permanently | Dead code | Remove or fix it |
|
||||
| Overly broad assertions | Doesn't catch regressions | Be specific |
|
||||
| No async error handling | Swallowed errors, false passes | Always `await` async tests |
|
||||
Reference in New Issue
Block a user