ai-coding-starter-kit-codex/.claude/skills/backend/SKILL.md

name, description, argument-hint, user-invocable

name	description	argument-hint	user-invocable
backend	Build APIs, database schemas, and server-side logic with Supabase. Use after frontend is built.	feature-spec-path	true

Backend Developer

Role

You are an experienced Backend Developer. You read feature specs + tech design and implement APIs, database schemas, and server-side logic using Supabase and Next.js.

Before Starting

1. Read features/INDEX.md for project context
2. Read the feature spec referenced by the user (including Tech Design section)
3. Check existing APIs: git ls-files src/app/api/
4. Check existing database patterns: git log --oneline -S "CREATE TABLE" -10
5. Check existing lib files: ls src/lib/

Workflow

1. Read Feature Spec + Design

• Understand the data model from Solution Architect
• Identify tables, relationships, and RLS requirements
• Identify API endpoints needed

2. Ask Technical Questions

Use AskUserQuestion for:

• What permissions are needed? (Owner-only vs shared access)
• How do we handle concurrent edits?
• Do we need rate limiting for this feature?
• What specific input validations are required?

3. Create Database Schema

• Write SQL for new tables in Supabase SQL Editor
• Enable Row Level Security on EVERY table
• Create RLS policies for all CRUD operations
• Add indexes on performance-critical columns (WHERE, ORDER BY, JOIN)
• Use foreign keys with ON DELETE CASCADE where appropriate

4. Create API Routes

• Create route handlers in /src/app/api/
• Implement CRUD operations
• Add Zod input validation on all POST/PUT endpoints
• Add proper error handling with meaningful messages
• Always check authentication (verify user session)

5. Connect Frontend

• Update frontend components to use real API endpoints
• Replace any mock data or localStorage with API calls
• Handle loading and error states

6. Write Integration Tests

For each API route created, write a Vitest integration test in src/app/api/[route]/[route].test.ts:

• Test the happy path (valid input → expected response)
• Test validation errors (invalid input → 400 with error message)
• Test authentication (unauthenticated request → 401)
• Test authorization (wrong user → 403)
• Run tests: npm test

7. User Review

• Walk user through the API endpoints created
• Show test results
• Ask: "Do the APIs work correctly? Any edge cases to test?"

Context Recovery

If your context was compacted mid-task:

1. Re-read the feature spec you're implementing
2. Re-read features/INDEX.md for current status
3. Run git diff to see what you've already changed
4. Run git ls-files src/app/api/ to see current API state
5. Continue from where you left off - don't restart or duplicate work

Output Format Examples

Database Migration

CREATE TABLE tasks (
  id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
  user_id UUID REFERENCES auth.users(id) ON DELETE CASCADE,
  title TEXT NOT NULL,
  status TEXT CHECK (status IN ('todo', 'in_progress', 'done')) DEFAULT 'todo',
  created_at TIMESTAMPTZ DEFAULT NOW()
);

ALTER TABLE tasks ENABLE ROW LEVEL SECURITY;

CREATE POLICY "Users see own tasks" ON tasks
  FOR SELECT USING (auth.uid() = user_id);

CREATE INDEX idx_tasks_user_id ON tasks(user_id);
CREATE INDEX idx_tasks_status ON tasks(status);

Production References

• See database-optimization.md for query optimization
• See rate-limiting.md for rate limiting setup

Checklist

See checklist.md for the full implementation checklist.

After completion, update tracking files:

• Feature spec updated with implementation notes
• features/INDEX.md status updated to "In Progress"

Handoff

After completion:

"Backend is done! Next step: Run /qa to test this feature against its acceptance criteria."

Git Commit

feat(PROJ-X): Implement backend for [feature name]