Firenook Swaps Firebase's Java Emulators for Rust, No Config Changes

Firenook, an open-source Rust replacement for the Firebase Local Emulator Suite, reached 171 points on Hacker News on Nov. 5. It runs Firestore, Authentication, Cloud Storage and Cloud Functions from your existing firebase.json, with no Java install. Teams that lose time to slow or memory-hungry emulator runs can swap one command and compare (Firenook).

What It Replaces

Firebase’s install documentation lists Node.js 16 or higher and Java JDK 11 or higher as prerequisites for the Local Emulator Suite. Firenook drops the Java requirement. It keeps the same ports and the same export format, and firebase-tools stays installed for deploys. In an npm script, firebase emulators:start becomes firenook emulators:start.

The Firenook site lists support for Firestore, Authentication, Cloud Storage, Cloud Functions, Extensions, Pub/Sub, Cloud Tasks and Eventarc. Realtime Database, Hosting, App Hosting and Data Connect are not emulated. A firebase.json that configures them still starts, with a warning. The current release is 0.2.1, and the Firenook team calls 0.2.0 its first release for public use.

The Numbers Are the Vendor’s

Firenook published its own benchmark, run Oct. 21 and 22 against firebase-tools 15.22.0 on Java 26. It used one server and one production web application with 211,205 Firestore documents. Median write latency was 5.1 ms against 208.2 ms for the official emulator. Peak memory was 2.11 GiB against 22.57 GiB. A restart with data kept took 0.59 seconds against 30.8 seconds.

Those are one team’s figures from one workload. The 40x headline is a median write time, not an overall speedup, so run it on your own data before moving CI over.

What Developers Said

The Hacker News thread was mostly praise. One commenter said Google had neglected the emulator experience. Another said they would “seriously consider switching” their team if application integrations ran on it. A third pointed to a separate open-source Rust project, Lark, as a basis for Realtime Database support.

The Take

This is opinion, kept apart from the reporting above. The emulators cost nothing to run and are easy to outgrow, so a faster one matters most to teams with large seed datasets. Coverage will decide adoption. Any project that relies on Realtime Database or Hosting emulation still needs the official suite, and a 0.2 release is young.