The fast, open-source terminal coding agent. ChooChoo generates AGENTS.md so every autonomous coding session follows your team's architectural decisions and security guardrails from session zero.
OpenCode reads AGENTS.md at startup to understand the project. ChooChoo compiles it from your actual codebase — covering architecture, key files, rules, and hard limits — so the agent starts fast and stays safe.
AGENTS.md with project structure, key files, and rules
Explicit ALWAYS / NEVER guardrails for safe autonomous operation
Stays in sync with your codebase as it evolves
# AGENTS.md
# Generated by ChooChoo — do not edit by hand.
## payments-api
FastAPI service · Python 3.12 · PostgreSQL
## Quick Context
src/ Main application code
src/api/ Route definitions
src/services/ Business logic
src/models/ SQLAlchemy ORM models
tests/ Mirrors src/ structure
## Rules
ALWAYS:
✓ Use SQLAlchemy ORM (never raw SQL)
✓ Annotate function signatures with types
✓ Write tests for new business logic
✓ Use environment variables for secrets
NEVER:
✗ Log secrets, tokens, or card data
✗ Modify files under migrations/ directly
✗ Skip Pydantic validation at API boundaries
## Key Files
src/main.py FastAPI entry point
src/auth/service.py JWT auth (ADR-001)
src/payments/ Stripe integration
src/db/session.py Database dependency
# SKILLS.md
# Generated by ChooChoo — do not edit by hand.
## auth
JWT token lifecycle: creation, validation, refresh.
Entry: src/auth/service.py
Tests: tests/auth/
## payments
Stripe integration: charges, subscriptions, webhooks.
Entry: src/payments/processor.py
Note: Never log STRIPE_KEY or card numbers
## database
SQLAlchemy sessions and query patterns.
Entry: src/db/session.py
Rule: Always use get_db() dependency injection
## notifications
Email (SendGrid) and SMS (Twilio) dispatch.
Entry: src/notifications/dispatch.py
# PLAN.md
# Generated by ChooChoo — do not edit by hand.
## Goal
Refactor the authentication service to support
multi-factor authentication (MFA) via TOTP.
## Steps
1. [ ] Add TOTP secret column to users table
migration: src/db/migrations/0023_add_totp.py
2. [ ] Implement TOTP validation in auth service
src/auth/service.py → verify_totp()
3. [ ] Add /auth/mfa/setup and /auth/mfa/verify routes
src/api/auth.py
4. [ ] Write unit tests for new MFA paths
tests/auth/test_mfa.py (≥ 90% coverage)
5. [ ] Update AGENTS.md with new ADR-012
## Constraints
- Do not break existing JWT flow (ADR-001)
- TOTP secrets encrypted at rest (AES-256)
- Rate-limit /auth/mfa/verify to 5 attempts / 15 min
# ARCHITECTURE.md
# Generated by ChooChoo — do not edit by hand.
## System Overview
payments-api is a stateless FastAPI service.
All state lives in PostgreSQL (primary data) and
Redis (sessions, rate limiting, event streams).
## Request Flow
Client → API Gateway → FastAPI → Service Layer
→ Repository Layer
→ PostgreSQL / Redis
## Key Modules
src/auth/ JWT issuance + TOTP (ADR-001, ADR-012)
src/payments/ Stripe integration (charges, webhooks)
src/db/ SQLAlchemy sessions + migration runner
src/api/ Route definitions (v1 + v2 namespaces)
## ADR Index
ADR-001 RS256 JWT for authentication
ADR-004 Redis Streams for webhook event bus
ADR-007 URL versioning (/v1/, /v2/)
ADR-012 TOTP-based MFA (in progress)
## Deployment
Docker → ECS Fargate (app)
RDS PostgreSQL 15 (primary)
ElastiCache Redis 7 (cache + streams)
# GOAL.md
# Generated by ChooChoo — do not edit by hand.
## Current Sprint Goal
Implement MFA support without breaking existing
single-factor authentication flows.
## Success Criteria
- All existing auth tests continue to pass
- New /auth/mfa/* endpoints return correct responses
- TOTP validation rejects tokens older than 30 s
- Coverage for src/auth/ stays above 90%
## Out of Scope
- SMS-based MFA (deferred to ADR-013)
- Admin UI for MFA management (separate ticket)
- Recovery codes (phase 2)
## Definition of Done
- PR reviewed and approved
- CI green (lint + test + coverage)
- AGENTS.md updated with ADR-012 summary
- Deployed to staging and smoke-tested
flowchart TD
A([Client Request]) --> B[API Gateway]
B --> C{JWT Valid?}
C -- Yes --> D[FastAPI Router]
C -- No --> E([401 Unauthorized])
D --> F[Service Layer]
F --> G[Repository]
G --> H[(PostgreSQL)]
G --> I[(Redis)]
F --> J[Stripe API]
J --> K[Webhook Event]
K --> L[(Redis Streams)]
Why use ChooChoo with OpenCode?
Fast autonomous agents need firm guardrails. ChooChoo gives OpenCode the structure to move quickly and safely.
Consistent Output
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Fewer Iterations
The AI understands your standards upfront, producing acceptable code faster and with less back-and-forth.
Team Alignment
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Zero Configuration
Get started instantly with sensible defaults that work out of the box for most projects.
Type-Safe Code
Strict linting rules catch potential bugs and enforce type safety before they reach review.
AI-Ready Rules
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