Official documentation of the itty ecosystem.

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welcome to

The itty ecosystem was born from a fun little experiment: To create the world’s smallest, full-featured JavaScript microrouter for use in edge/client environments where bundle size matters. Thus itty-router was born.

Each of the additional libraries were later developed to support other elements of API generation.

We remove boilerplate noise through high-impact, low-calorie microlibraries.

By creating minimalist (yet flexible) versions of common patterns, we’ve made low-cost alternatives to many current larger libraries we all use. Some of these we’ve written countless times in our own projects (e.g. itty-fetcher or itty-time), as certainly you’ve done as well.

The catch? We also aim to make them even smaller than you might write yourself, making them a guiltless inclusion within each project!

the lineup:

itty-router - itty-router

At only 450 bytes, itty-router is arguably the world’s smallest, feature-rich router, designed for use in nearly any environment or runtime. It has two goals in mind: 1. have nearly zero impact on your bundle sizes, and 2. keep your API code looking tiny and beautiful.

It gets top billing because it was the first, the OG “itty”.

import { 
  error,              // creates error Responses
  json,               // creates JSON Responses
  Router,             // the Router itself
} from 'itty-router'

const router = Router()

  // GET a route, with a route param
    ({ params }) => ({ message: `You fetched todo #${}` })

  // *any* HTTP method works, even ones you make up
  .puppy('/secret', () => 'Because why not?')

  // return a 404 for anything else
  .all('*', () => error(404))

// Example showing Cloudflare module syntax
export default {
  fetch: (req, env, ctx) => router
                              .handle(req, env, ctx)
                              .then(json)   // turn any raw data into JSON
                              .catch(error) // and catch any uncaught errors

itty-fetcher - itty-fetcher

The same boilerplate native Fetch API helper you’ve probably written dozens of times - just hopefully a bit smaller, allowing you to write your fetch calls like this:

// optionally predefine an API
const api = fetcher({ base: '' })

// GET some JSON (everything is auto-parsed by default)
const data = await api.get('/my/json/api')

// or POST some data
await'/my/collection', { foo: 'bar' })

itty-time - itty-time

So you’ve written an API but need to calculate max-age, expirations, etc. This library simplifies the process, allowing you to write durations such as “1 week, 2 days, and 4 hours” instead of… 1000 * 60 * 60 * 24 * 7 + 1000 * 60 * 60 * 24 * 2 + 1000 * 60 * 60… well, you get the point. All this is done in about 500 bytes.

// get seconds for TTL
const ttl = getSeconds('1 month and 30 minutes')

// or get a future date
const expiration = datePlus('1 week')

// or a future date from another date
const expiration = datePlus('1 week', datePlus('1 year'))

itty-durable - itty-durable

A bit of an experimental package, designed to allow a [much] more direct usage of Cloudflare Durable Object. This library removes virtually all boilerplate when working with DOs, leaving your code tiny, readable, and powerful.

Now your Durable Object class can look this simple:

import { createDurable } from 'itty-durable'

export class Counter extends createDurable({ autoReturn: true, autoPersist: true }) {
  constructor(state, env) {
    super(state, env)
    this.counter = 0

  increment() {

  setValue(newValue: number) {
    this.counter = newValue

While being able to access them from a Worker much like a native class:

import { Router, error, withParams } from 'itty-router'
import { withDurables } from 'itty-durable'

// export the durable class, per spec
export { Counter } from './Counter'

const router = Router()

  // add upstream middleware
  .all('*', withDurables(), withParams)

  // get the contents of a DO
  .get('/:id', ({ id, Counter }) => 

  // call a method on the DC
  .get('/:id/increment', ({ id, Counter }) => 

  // or pass data to a method
  .get('/set/:value', withParams, ({ id, value, Counter }) =>