# facebook/hermes

A JavaScript engine optimized for running React Native.

Repository: https://github.com/facebook/hermes
Canonical: https://ross.abutalabs.com/products/hermes
Language: JavaScript
License: MIT
License Family: permissive
Last push: 2026-08-26T17:46:27+00:00

## Health v2 (maintenance only)
Score: 67/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 8, longevity 100
- inputs: {"age_days": 2872, "days_push": 7, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 11272, forks 847 (observed 2026-08-28T04:10:46.624050+00:00)

## What it is
Hermes is a JavaScript engine developed by Meta, optimized for fast start-up of React Native apps through ahead-of-time static optimization and compact bytecode. It can be built as CLI tools to run JavaScript directly and is the default engine for React Native.

## Use cases
- run react native apps with faster startup time
- embed a lightweight javascript engine in a mobile app
- compile javascript to compact bytecode ahead of time
- reduce memory usage of a javascript runtime on mobile
- build and hack on a javascript engine from source
- run javascript from the command line

## When to avoid
- you need a general-purpose Node.js-compatible JavaScript runtime
- your project depends on Node.js APIs or npm ecosystem at runtime
- you need the latest ECMAScript features immediately, as Hermes lags V8/JSC in some support

## Facets
- artifact type: library
- maturity: active
- function: interpreter, compiler, developer-tools
- domain: mobile-development, programming-languages, compilers, performance
- platform: windows, cpp
- tags: javascript-engine, react-native, bytecode, aot-optimization, runtime, android, ios, macos, linux

## Member repositories
- facebook/hermes (main) score 67

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:10:46.624050+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T17:16:00.096682+00:00, confidence not recorded.
  - readme: https://github.com/facebook/hermes (fetched 2026-08-28T04:10:46.624050+00:00, sha 2bf480382ea9)
- Data as of 2026-08-30T08:39:29.467469+00:00.