01 · CLI shim
rjest binary
A thin Rust CLI. It opens a Unix domain socket to jestd, forwards your args, streams results back, and renders Jest-style output. If the daemon is not running, it boots one.
Architecture
How rjest stays warm
Every rjest run is a request to a long-lived daemon. Understanding the five stages below explains exactly where the warm-run speedup comes from — and why cold start is honestly a little slower.
rjest --watch you type this │ nng / Unix domain socket (sub-ms) ▼ ┌──────────────────────────────────────────┐ │ jestd (persistent Rust daemon) │ │ ├─ parsed jest.config (in memory) │ │ ├─ dependency graph (in memory) │ │ ├─ FS watcher (live) │ │ ├─ SWC transforms ──▶ sled cache (blake3) │ │ └─ worker pool ──▶ warm Node.js VMs │ └──────────────────────────────────────────┘ │ ▼ PASS src/*.test.ts rendered Jest-style
02 · Transport
nng socket
nanomsg-next-gen over a Unix domain socket. Sub-millisecond round-trip between the CLI and the daemon — the request/response cost is effectively free.
03 · Daemon
jestd
Holds the parsed Jest config, the file-system watcher, the module dependency graph, and the worker pool. It is the thing that survives between invocations.
04 · Transforms
SWC + sled
TypeScript and JSX compiled natively by SWC. Output cached in sled on disk, keyed by blake3 content hash. A file only re-transforms when its bytes change.
05 · Workers
Warm Node.js pool
Persistent Node processes execute test files in isolated VM contexts. V8 warmup and JIT are amortized across runs instead of paid per invocation.
Why cold start is slower
The first invocation in a session has to boot the daemon, spin up workers, and warm V8. That is why the repo benchmark shows rjest at ~1.9s cold versus Jest's ~1.4s. You pay it once. Every subsequent run reuses the warm daemon and lands in milliseconds. Most of CI and all of local watch-mode development live in the warm path — which is exactly what rjest optimizes.
Why the cache survives restarts
Transform output is content-addressed. When you restart jestd (or reboot), the sled store on disk is still valid because a blake3 hash of the source bytes maps deterministically to the compiled result. A cold restart therefore skips re-transforming anything that has not changed.
Read the guides for practical setup, or the deep dive on where Jest's time actually goes.