Metro is a Fetch-compatible HTTP client with middleware. It keeps the browser's Request, Response, URL, and FormData model, then adds a small set of conveniences: reusable clients, immutable .with() helpers, middleware composition, API helpers, tracing, and optional packages for OAuth2, OpenID Connect, and Linked Data.

Most applications should start with the combined package:

npm install @muze-nl/metro

import metro from '@muze-nl/metro'

const client = metro.client('https://jsonplaceholder.typicode.com/')
  .with(metro.mw.json())

const response = await client.get('/posts/1')
console.log(response.data.title)

For a browser page without a bundler, use the browser bundle. It creates globalThis.metro:

<script src="https://cdn.jsdelivr.net/npm/@muze-nl/metro@0.7.1/dist/browser.min.js"></script>
<script>
  const client = metro.client('https://jsonplaceholder.typicode.com/')
    .with(metro.mw.json())

  client.get('/posts/1').then(response => {
    console.log(response.data.title)
  })
</script>

Advanced applications can install only the packages they need:

npm install @muze-nl/metro-core @muze-nl/metro-middleware

import { client } from '@muze-nl/metro-core'
import { json, retry, timeout } from '@muze-nl/metro-middleware'

const api = client('https://jsonplaceholder.typicode.com/')
  .with(timeout(5000), retry({ attempts: 3 }), json())

General documentation that applies across packages lives in docs/:

• docs/quickstart.md — install Metro and make the first request.
• docs/tutorial.md — longer guided tutorial.
• docs/packages.md — package map and import choices.
• docs/debugging.md — tracing and diagnostics across Metro clients.
• docs/details/ — error and diagnostic detail pages used by Metro error messages.

Package-specific installation, usage, and reference documentation lives beside each package:

npm install
npm test
npm run build

Useful focused commands:

npm run test:core
npm run test:oauth2

Mock OAuth2/OIDC servers are test helpers. Import them from explicit testing entries so they do not inflate production browser bundles:

import oauth2mockserver from '@muze-nl/metro-oauth2/testing'
import oidcmockserver from '@muze-nl/metro-oidc/testing'

@muze-nl/metro-core should stay small. Generic middleware belongs in @muze-nl/metro-middleware, tracing belongs in @muze-nl/metro-trace, beginner convenience belongs in @muze-nl/metro, and auth or Linked Data behaviour belongs in its own package.