Live Mode

Live mode serves React projects directly from source with on-demand compilation. There is no build step — Rex compiles on the first request, caches the result, and automatically recompiles when source files change.

Quick start

rex live -m /=./my-app

This starts a server on port 4000 that serves my-app at the root path. The first request triggers compilation; subsequent requests use the cached build until source files change.

Mounting multiple projects

Mount several projects under different URL prefixes to serve them from a single server:

rex live \
  -m /=./marketing-site \
  -m /dashboard=./admin-app \
  -m /docs=./docs-site

Requests are matched by longest prefix first, so /dashboard/settings routes to the admin app while /about routes to the marketing site.

Each mounted project is fully isolated — it gets its own build cache, V8 isolate pool, route trie, and file watcher.

Options

How it works

1. First request — Rex scans the project's pages/ or app/ directory, bundles with Rolldown, initializes a V8 isolate pool, and serves the response. The compilation result is cached.
2. Subsequent requests — Rex checks source file timestamps. If nothing changed, the cached build is used immediately. If a file changed, Rex recompiles before serving.
3. File watcher — A background file watcher proactively invalidates the build cache when source files change, so the next request triggers a fresh build without waiting for a timestamp check.

Cache invalidation

Live mode uses timestamp-based invalidation by default. On every request, Rex walks the source directories and compares file modification times against the cached build. This is zero-config and works with any deployment method.

The file watcher acts as a belt-and-suspenders mechanism — it invalidates the cache immediately on file changes so the next request doesn't need to wait for the timestamp walk.

Use cases

• Agent-friendly deployments — push source files to a directory and they're live immediately, no CI/CD pipeline needed
• Multi-tenant serving — mount different teams' apps under isolated prefixes on a single server
• Rapid prototyping — skip the build step during development without running a full dev server
• Micro-frontend replacement — serve multiple independent React apps from one server without the complexity of module federation

Comparison with other modes