/expo-api-routes

name: expo-api-routes
description: Guidelines for creating API routes in Expo Router with EAS Hosting
version: 1.0.0
license: MIT
domain: engineering

When to Use API Routes

Use API routes when you need:

• **Server-side secrets** — API keys, database credentials, or tokens that must never reach the client
• **Database operations** — Direct database queries that shouldn't be exposed
• **Third-party API proxies** — Hide API keys when calling external services (OpenAI, Stripe, etc.)
• **Server-side validation** — Validate data before database writes
• **Webhook endpoints** — Receive callbacks from services like Stripe or GitHub
• **Rate limiting** — Control access at the server level
• **Heavy computation** — Offload processing that would be slow on mobile

When NOT to Use API Routes

Avoid API routes when:

• **Data is already public** — Use direct fetch to public APIs instead
• **No secrets required** — Static data or client-safe operations
• **Real-time updates needed** — Use WebSockets or services like Supabase Realtime
• **Simple CRUD** — Consider Firebase, Supabase, or Convex for managed backends
• **File uploads** — Use direct-to-storage uploads (S3 presigned URLs, Cloudflare R2)
• **Authentication only** — Use Clerk, Auth0, or Firebase Auth instead

File Structure

API routes live in the `app` directory with `+api.ts` suffix:

app/
  api/
    hello+api.ts          → GET /api/hello
    users+api.ts          → /api/users
    users/[id]+api.ts     → /api/users/:id
  (tabs)/
    index.tsx

Basic API Route

// app/api/hello+api.ts
export function GET(request: Request) {
  return Response.json({ message: "Hello from Expo!" });
}

HTTP Methods

Export named functions for each HTTP method:

// app/api/items+api.ts
export function GET(request: Request) {
  return Response.json({ items: [] });
}

export async function POST(request: Request) {
  const body = await request.json();
  return Response.json({ created: body }, { status: 201 });
}

export async function PUT(request: Request) {
  const body = await request.json();
  return Response.json({ updated: body });
}

export async function DELETE(request: Request) {
  return new Response(null, { status: 204 });
}

Dynamic Routes

// app/api/users/[id]+api.ts
export function GET(request: Request, { id }: { id: string }) {
  return Response.json({ userId: id });
}

Request Handling

Query Parameters

export function GET(request: Request) {
  const url = new URL(request.url);
  const page = url.searchParams.get("page") ?? "1";
  const limit = url.searchParams.get("limit") ?? "10";

  return Response.json({ page, limit });
}

Headers

export function GET(request: Request) {
  const auth = request.headers.get("Authorization");

  if (!auth) {
    return Response.json({ error: "Unauthorized" }, { status: 401 });
  }

  return Response.json({ authenticated: true });
}

JSON Body

export async function POST(request: Request) {
  const { email, password } = await request.json();

  if (!email || !password) {
    return Response.json({ error: "Missing fields" }, { status: 400 });
  }

  return Response.json({ success: true });
}

Environment Variables

Use `process.env` for server-side secrets:

// app/api/ai+api.ts
export async function POST(request: Request) {
  const { prompt } = await request.json();

  const response = await fetch("https://api.openai.com/v1/chat/completions", {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${process.env.OPENAI_API_KEY}`,
    },
    body: JSON.stringify({
      model: "gpt-4",
      messages: [{ role: "user", content: prompt }],
    }),
  });

  const data = await response.json();
  return Response.json(data);
}

Set environment variables:

• **Local**: Create `.env` file (never commit)
• **EAS Hosting**: Use `eas env:create` or Expo dashboard

CORS Headers

Add CORS for web clients:

const corsHeaders = {
  "Access-Control-Allow-Origin": "*",
  "Access-Control-Allow-Methods": "GET, POST, PUT, DELETE, OPTIONS",
  "Access-Control-Allow-Headers": "Content-Type, Authorization",
};

export function OPTIONS() {
  return new Response(null, { headers: corsHeaders });
}

export function GET() {
  return Response.json({ data: "value" }, { headers: corsHeaders });
}

Error Handling

export async function POST(request: Request) {
  try {
    const body = await request.json();
    // Process...
    return Response.json({ success: true });
  } catch (error) {
    console.error("API error:", error);
    return Response.json({ error: "Internal server error" }, { status: 500 });
  }
}

Testing Locally

Start the development server with API routes:

npx expo serve

This starts a local server at `http://localhost:8081` with full API route support.

Test with curl:

curl http://localhost:8081/api/hello
curl -X POST http://localhost:8081/api/users -H "Content-Type: application/json" -d '{"name":"Test"}'

Deployment to EAS Hosting

Prerequisites

npm install -g eas-cli
eas login

Deploy

eas deploy

This builds and deploys your API routes to EAS Hosting (Cloudflare Workers).

Environment Variables for Production

# Create a secret
eas env:create --name OPENAI_API_KEY --value sk-xxx --environment production

# Or use the Expo dashboard

Custom Domain

Configure in `eas.json` or Expo dashboard.

EAS Hosting Runtime (Cloudflare Workers)

API routes run on Cloudflare Workers. Key limitations:

Missing/Limited APIs

• **No Node.js filesystem** — `fs` module unavailable
• **No native Node modules** — Use Web APIs or polyfills
• **Limited execution time** — 30 second timeout for CPU-intensive tasks
• **No persistent connections** — WebSockets require Durable Objects
• **fetch is available** — Use standard fetch for HTTP requests

Use Web APIs Ins