Concepts

Async Web keeps the original runtime model: standard Request objects enter a route graph and standard Response objects come back.

Apps

An app is a browser-safe FetchApp:

const api = {
  fetch(request, env, context) {
    return Response.json({
      pathname: new URL(request.url).pathname
    });
  }
};

Apps can represent browser documents/assets, origin handlers, AsyncDB adapters, service-worker behavior, edge middleware, or local test fixtures. In @async/web, builders such as browserApp(), fetchApp(), and asyncDbApp() all normalize to the same internal FetchApp shape.

Routes

Routes are structured specs in @async/web/router. They decide whether a request is mounted, redirected, cached, proxied to an origin, served from files, or sent to an app. @async/web lowers those specs into WebRuntime middleware when it builds the executable runtime config.

routes: [
  mount('/db', toApp('db')),
  mount('/api', toApp('api')),
  toApp('web')
]

Platform

Each runtime environment owns scoped platform APIs. platform.fetch() resolves relative URLs from the current app location and re-enters the same route graph.

Packages

Use @async/web for app defaults and deployment-oriented configuration. Use @async/web/router for structured route inspection and composition. Use @async/web/runtime when runtime execution, cache behavior, platform context, or provider placement needs to be explicit.