versionkit

Framework-agnostic API versioning with full RFC compliance.

Supports RFC 8594 (Sunset header), RFC 9745 (Deprecation header), and three version extraction strategies. Works with Hono, Fastify, Express, and any framework using Web Standards Request/Response.

Why

APIs evolve. Clients need time to migrate. versionkit gives you:

• Version routing - dispatch requests to the right handler based on version
• Deprecation signals - automatically inject RFC-compliant headers so clients know when versions are going away
• Framework freedom - built on Web Standards, works everywhere

Install

npm install versionkit

Strategies

Strategy	Source	Example
header	Custom request header	Api-Version: 2025-01-01
url	URL path prefix	/v2/users
accept	Accept header media type	application/vnd.api.v2+json

Usage

Header Strategy

import { createVersionRouter } from 'versionkit';

const router = createVersionRouter({
  strategy: 'header',
  headerName: 'Api-Version', // default
  defaultVersion: '1',
  versions: {
    '1': {
      deprecated: true,
      deprecation: {
        sunset: new Date('2026-06-01'),
        deprecatedSince: new Date('2025-01-01'),
        link: 'https://docs.example.com/changelog',
      },
    },
    '2': {},
  },
});

router
  .handle('1', (req) => new Response(JSON.stringify({ version: 1 })))
  .handle('2', (req) => new Response(JSON.stringify({ version: 2 })));

const handler = router.middleware();
// handler(request) => Promise<Response>

URL Strategy

const router = createVersionRouter({
  strategy: 'url',
  versions: { '1': {}, '2': {} },
});

router
  .handle('1', () => new Response('v1'))
  .handle('2', () => new Response('v2'));

// GET /v2/users -> dispatches to version "2" handler

Accept Header Strategy

const router = createVersionRouter({
  strategy: 'accept',
  versions: { 'v1': {}, 'v2': {} },
});

router
  .handle('v1', () => new Response('v1'))
  .handle('v2', () => new Response('v2'));

// Accept: application/vnd.api.v2+json -> dispatches to "v2" handler

RFC Compliance

RFC 8594 - Sunset Header

When a version has a sunset date, the response includes:

Sunset: Mon, 01 Jun 2026 00:00:00 GMT

When a link is provided, the response includes:

Link: <https://docs.example.com/changelog>; rel="deprecation"

RFC 9745 - Deprecation Header

When deprecatedSince is set:

Deprecation: @1735689600

When no date is specified but the version is deprecated:

Deprecation: true

Framework Integration

Hono

import { Hono } from 'hono';
import { createVersionRouter } from 'versionkit';

const app = new Hono();
const router = createVersionRouter({ strategy: 'header', versions: { '1': {} } });
router.handle('1', (req) => new Response('v1'));

app.all('/api/*', (c) => router.middleware()(c.req.raw));

Express

import express from 'express';
import { createVersionRouter } from 'versionkit';

const app = express();
const router = createVersionRouter({ strategy: 'header', versions: { '1': {} } });
router.handle('1', (req) => new Response('v1'));

const handler = router.middleware();

app.use('/api', async (req, res) => {
  const webReq = new Request(`http://${req.headers.host}${req.url}`, {
    method: req.method,
    headers: req.headers as any,
  });
  const webRes = await handler(webReq);
  res.status(webRes.status);
  webRes.headers.forEach((v, k) => res.setHeader(k, v));
  res.send(await webRes.text());
});

Fastify

import Fastify from 'fastify';
import { createVersionRouter } from 'versionkit';

const fastify = Fastify();
const router = createVersionRouter({ strategy: 'url', versions: { '1': {} } });
router.handle('1', (req) => new Response('v1'));

const handler = router.middleware();

fastify.all('/v*', async (req, reply) => {
  const webReq = new Request(`http://${req.hostname}${req.url}`, {
    method: req.method,
    headers: req.headers as any,
  });
  const webRes = await handler(webReq);
  reply.status(webRes.status);
  webRes.headers.forEach((v, k) => reply.header(k, v));
  reply.send(await webRes.text());
});

API

createVersionRouter(opts: VersionRouterOptions): VersionRouter

Creates a new version router.

VersionRouter.handle(version: string, handler: RequestHandler): this

Registers a handler for a specific version. Chainable.

VersionRouter.middleware(): (req: Request) => Promise<Response>

Returns a request handler that dispatches to the correct versioned handler.

VersionRouter.resolveVersion(req: Request): string | null

Resolves which version applies to a given request without dispatching.

License

MIT