version: "1.0.2" name: netlify-functions description: Guide for writing Netlify serverless functions. Use when creating API endpoints, background processing, scheduled tasks, or any server-side logic using Netlify Functions. Covers modern syntax (default export + Config), TypeScript, path routing, background functions, scheduled functions, streaming, and method routing.

Netlify Functions

Modern Syntax

Always use the modern default export + Config pattern. Never use the legacy exports.handler or named handler export.

import type { Context, Config } from "@netlify/functions";
export default async (req: Request, context: Context) => {
  return new Response("Hello, world!");
};
export const config: Config = {
  path: "/api/hello",
};

The handler receives a standard Web API Request and returns a Response. The second argument is a Netlify Context object.

File Structure

Place functions in netlify/functions/:

netlify/functions/
  _shared/           # Non-function shared code (underscore prefix)
    auth.ts
    db.ts
  items.ts           # -> /.netlify/functions/items (or custom path via config)
  users/index.ts     # -> /.netlify/functions/users

Use .ts or .mts extensions. If both .ts and .js exist with the same name, the .js file takes precedence.

Path Routing

Define custom paths via the config export:

export const config: Config = {
  path: "/api/items",                    // Static path
  // path: "/api/items/:id",            // Path parameter
  // path: ["/api/items", "/api/items/:id"], // Multiple paths
  // excludedPath: "/api/items/special", // Excluded paths
  // preferStatic: true,                // Don't override static files
};

Without a path config, functions are available at /.netlify/functions/{name}. Setting a path makes the function available only at that path.

Access path parameters via context.params:

// config: { path: "/api/items/:id" }
export default async (req: Request, context: Context) => {
  const { id } = context.params;
  // ...
};

Method Routing

export default async (req: Request, context: Context) => {
  switch (req.method) {
    case "GET":    return handleGet(context.params.id);
    case "POST":   return handlePost(await req.json());
    case "DELETE": return handleDelete(context.params.id);
    default:       return new Response("Method not allowed", { status: 405 });
  }
};
export const config: Config = {
  path: "/api/items/:id",
  method: ["GET", "POST", "DELETE"],
};

Background Functions

For long-running tasks (up to 15 minutes). The client receives an immediate 202 response; return values are ignored.

Name the file with a -background suffix:

netlify/functions/process-background.ts

Store results externally (Netlify Blobs, database) for later retrieval.

Scheduled Functions

Run on a cron schedule (UTC timezone):

export default async (req: Request) => {
  const { next_run } = await req.json();
  console.log("Next invocation at:", next_run);
};
export const config: Config = {
  schedule: "@hourly", // or cron: "0 * * * *"
};

Shortcuts: @yearly, @monthly, @weekly, @daily, @hourly. Scheduled functions have a 30-second timeout and only run on published deploys.

Streaming Responses

Return a ReadableStream body for streamed responses (up to 20 MB):

export default async (req: Request) => {
  const stream = new ReadableStream({ /* ... */ });
  return new Response(stream, {
    headers: { "Content-Type": "text/event-stream" },
  });
};

Context Object

Environment Variables

Use Netlify.env (not process.env) inside functions:

const apiKey = Netlify.env.get("API_KEY");

Resource Limits

Framework Considerations

Frameworks with server-side capabilities (Astro, Next.js, Nuxt, SvelteKit, TanStack Start) typically generate their own serverless functions via adapters. You usually do not write raw Netlify Functions in these projects — the framework adapter handles server-side rendering and API routes. Write Netlify Functions directly when:

• Using a client-side-only framework (Vite + React SPA, vanilla JS)
• Adding background or scheduled tasks to any project
• Building standalone API endpoints outside the framework's routing

See the netlify-frameworks skill for adapter setup.