Scaffold Backend

Scaffold Backend

This skill creates the backend for the user's project inside a server/ directory at the repo root. Like scaffold-frontend, it is driven entirely by PRD.md and AGENTS.md. Every route, every Pydantic model, and the decision to include Supabase are all derived from the PRD.

Preflight: PRD, AGENTS, and Backend Needed

Before doing anything else, check three conditions:

1. AGENTS.md exists at the repo root.
2. PRD.md exists at the repo root.
3. PRD.md > Backend Needed? starts with Yes.

test -f AGENTS.md && test -f PRD.md || { echo "MISSING_DOCS"; exit 1; }
grep -A1 "^## Backend Needed?" PRD.md | tail -n1

Fail-fast responses

• If AGENTS.md or PRD.md is missing, STOP and respond exactly:

  This skill cannot run yet. AGENTS.md and PRD.md must exist at the repo root. Run the domain-to-spec skill first, or run the quickstart skill to chain everything automatically.

• If Backend Needed? is No (or empty), STOP and respond exactly:

  This project does not need a backend according to PRD.md > Backend Needed?. If that is wrong, rerun the domain-to-spec skill to update the PRD. Otherwise, run the feature-builder skill to build out frontend features.

Do not create any files in either fail case.

Step 1: Read the PRD and AGENTS

Extract from PRD.md:

• Routes list (from PRD.md > Backend Routes). Each bullet becomes a FastAPI route.
• Data model (from PRD.md > Data Model). Each entity becomes a Pydantic model.
• Domain constraints (from PRD.md > Domain Constraints). Used to decide what validation rules to add.
• Auth requirement. Check if PRD.md > Core Features (MVP) or PRD.md > User Flow mention login, accounts, or user-specific data. If yes, Supabase Auth is needed.

Extract from AGENTS.md:

• The Python version and FastAPI conventions.
• Whether Supabase is listed under ## Tech Stack > Database.

Step 2: Ask About Supabase

Prompt the user:

"Your PRD implies this app needs a database. I recommend Supabase because it is free, hosted, and integrates auth, Postgres, and storage in one service. Should I wire it up now? (yes / no / later)"

• If yes: include Supabase integration in Step 4.
• If no: scaffold FastAPI only; use an in-memory Python dict as a placeholder store, with a clear TODO comment to swap it out later.
• If later: same as no.

Step 3: Scaffold server/

Create the following structure at the repo root:

server/
  app/
    __init__.py
    main.py                # FastAPI app entry point
    config.py              # Environment variable loader
    db.py                  # Supabase client or in-memory store
    models.py              # Pydantic models (from PRD Data Model)
    routes/
      __init__.py
      health.py            # GET /health
      <entity>.py          # One file per entity in the PRD (e.g. submissions.py)
  tests/
    __init__.py
    test_health.py
  .env.example
  .gitignore
  requirements.txt
  README.md

Step 4: Generate requirements.txt

Always include:

fastapi>=0.115
uvicorn[standard]>=0.32
pydantic>=2.9
pydantic-settings>=2.6
python-dotenv>=1.0
pytest>=8.3
httpx>=0.27

If Supabase was chosen, also include:

supabase>=2.9

Step 5: Generate main.py

from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

from app.routes import health
# Import one route module per entity in PRD > Backend Routes
# Example: from app.routes import submissions

app = FastAPI(title="{project name from PRD}")

app.add_middleware(
    CORSMiddleware,
    allow_origins=["http://localhost:3000"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

app.include_router(health.router)
# app.include_router(submissions.router, prefix="/submissions", tags=["submissions"])

Replace {project name from PRD} with the one-sentence summary's subject. Uncomment and add one include_router call per entity found in PRD.md > Backend Routes.

Step 6: Generate Pydantic Models From the Data Model

For each entity in PRD.md > Data Model, create a class in app/models.py:

from datetime import datetime
from typing import Literal
from pydantic import BaseModel, Field

class SubmissionBase(BaseModel):
    patient_name: str = Field(..., min_length=1)
    date: datetime
    medications: list[str]

class SubmissionCreate(SubmissionBase):
    pass

class Submission(SubmissionBase):
    id: str
    status: Literal["pending", "approved", "rejected"] = "pending"

Always generate a Base, a Create, and a full model per entity. This pattern gives you clean request/response separation.

Step 7: Generate Route Stubs From PRD.md > Backend Routes

For each bullet under PRD.md > Backend Routes, generate a FastAPI route. Example input:

- POST /submissions — create a new submission from the form
- GET /submissions — list the current user's submissions
- GET /submissions/{id} — fetch one submission
- POST /submissions/{id}/approve — mark a submission as approved

Generated app/routes/submissions.py:

from fastapi import APIRouter, HTTPException
from uuid import uuid4

from app.models import Submission, SubmissionCreate
from app.db import store

router = APIRouter()

@router.post("", response_model=Submission)
def create_submission(payload: SubmissionCreate) -> Submission:
    submission = Submission(id=str(uuid4()), **payload.model_dump())
    store.setdefault("submissions", {})[submission.id] = submission
    return submission

@router.get("", response_model=list[Submission])
def list_submissions() -> list[Submission]:
    return list(store.get("submissions", {}).values())

@router.get("/{submission_id}", response_model=Submission)
def get_submission(submission_id: str) -> Submission:
    submission = store.get("submissions", {}).get(submission_id)
    if submission is None:
        raise HTTPException(status_code=404, detail="Submission not found")
    return submission

@router.post("/{submission_id}/approve", response_model=Submission)
def approve_submission(submission_id: str) -> Submission:
    submission = store.get("submissions", {}).get(submission_id)
    if submission is None:
        raise HTTPException(status_code=404, detail="Submission not found")
    submission = submission.model_copy(update={"status": "approved"})
    store["submissions"][submission_id] = submission
    return submission

Every route should return dummy but type-safe data so the frontend has something to consume immediately.

Step 8: Generate db.py

If Supabase was chosen

from supabase import create_client, Client
from app.config import settings

supabase: Client = create_client(settings.supabase_url, settings.supabase_key)

Add to .env.example:

SUPABASE_URL=https://your-project.supabase.co
SUPABASE_KEY=your-anon-or-service-key

Add a short section to server/README.md explaining how to create a Supabase project, copy the URL and anon key, and paste them into .env.

If Supabase was declined

# Temporary in-memory store. Swap for Supabase/Postgres before production.
store: dict[str, dict] = {}

Step 9: Generate config.py and .env.example

app/config.py:

from pydantic_settings import BaseSettings, SettingsConfigDict

class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_file=".env", extra="ignore")

    supabase_url: str = ""
    supabase_key: str = ""

settings = Settings()

.env.example:

# Copy this file to .env and fill in your values
SUPABASE_URL=
SUPABASE_KEY=

Step 10: Generate tests/test_health.py

from fastapi.testclient import TestClient
from app.main import app

client = TestClient(app)

def test_health() -> None:
    response = client.get("/health")
    assert response.status_code == 200
    assert response.json() == {"status": "ok"}

And app/routes/health.py:

from fastapi import APIRouter

router = APIRouter()

@router.get("/health")
def health() -> dict[str, str]:
    return {"status": "ok"}

Step 11: Generate server/.gitignore

.venv/
__pycache__/
*.pyc
.env
.pytest_cache/
.coverage

Step 12: Generate server/README.md

A short README with:

• One-sentence project summary (from PRD).
• Setup: create venv, pip install -r requirements.txt, copy .env.example to .env.
• Run dev: uvicorn app.main:app --reload.
• Tests: pytest.
• If Supabase is wired up: a "Setting up Supabase" section with 4-5 bullet steps.

Step 13: Verify

From the repo root:

cd server
python -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt
uvicorn app.main:app --reload &
sleep 2
curl http://localhost:8000/health
pytest

Confirm:

• GET /health returns {"status": "ok"}.
• Every generated route appears in http://localhost:8000/docs (FastAPI auto-docs).
• pytest passes.

If anything fails, STOP and invoke the bugfix-doctor skill.

Output

Return exactly:

1. Files Created: Every file under server/, with a one-line description.
2. Routes Generated: One bullet per route, mapped to its entry in PRD.md > Backend Routes.
3. Supabase Wired Up?: Yes or No (with the reason the user gave).
4. Verification: Confirmation that /health responded, auto-docs listed every route, and tests passed.
5. Next Steps:
   • "Update client/.env.local with NEXT_PUBLIC_API_URL=http://localhost:8000."
   • "Run both servers together: cd server && uvicorn app.main:app --reload in one terminal, cd client && pnpm dev in another."
   • "Use the feature-builder skill to connect the first frontend page to the first backend route."

Rules

• Never run without AGENTS.md and PRD.md at the repo root.
• Never run if PRD.md > Backend Needed? is not Yes.
• Never overwrite an existing non-empty server/ directory without asking.
• Never invent routes that are not in PRD.md > Backend Routes. If the list is empty, ask the user to update the PRD first.
• Every route must return type-safe dummy data. No NotImplementedError stubs. The frontend should be able to call the backend end-to-end immediately after scaffolding.
• Never hardcode secrets. Use app/config.py + .env for every external key.