# facebook/flow

Adds static typing to JavaScript to improve developer productivity and code quality.

Repository: https://github.com/facebook/flow
Canonical: https://ross.abutalabs.com/products/flow
Homepage: https://flow.org/
Language: Rust
License: MIT
License Family: permissive
Last push: 2026-08-27T00:14:38+00:00

## Health v2 (maintenance only)
Score: 95/100 (v2, computed 2026-09-03T02:39:23.370411+00:00)
- activity 99, release rhythm 87, longevity 100
- inputs: {"age_days": 4327, "days_push": 7, "days_rel": 11, "gap_med": 5.0, "n_releases_24m": 111}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 22279, forks 1890 (observed 2026-08-28T04:11:32.513563+00:00)

## What it is
Flow is a static type checker for JavaScript, now a typed dialect of JavaScript written in Rust. It catches type errors via annotations and offers first-class React component syntax and pattern matching.

## Use cases
- add static typing to a JavaScript codebase
- type-check React components with first-class component syntax
- catch type errors before runtime in JS projects
- migrate from TypeScript to a stricter type checker
- strip Flow type annotations with Babel or flow-remove-types
- parse Flow-typed JavaScript to get an annotated syntax tree

## When to choose
- you want stronger static guarantees than TypeScript, like exact-by-default object types
- your project is React-heavy and benefits from component and renders syntax
- you want built-in pattern matching with exhaustiveness checks

## When to avoid
- your team and ecosystem already standardize on TypeScript
- you need a typechecker that also emits JavaScript (Flow requires a separate build step)
- you rely on TypeScript-only features or its much larger ecosystem

## Facets
- artifact type: cli-tool
- maturity: active
- function: type-system, linter, parser, cli, developer-tools
- domain: programming-languages, web-development, frontend, developer-tools
- platform: windows, cli
- tags: static-type-checker, javascript, react, typescript-alternative, rust, macos, linux, nodejs

## Member repositories
- facebook/flow (main) score 95

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:11:32.513563+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 2026-08-29T16:57:22.561291+00:00, confidence not recorded.
  - readme: https://github.com/facebook/flow (fetched 2026-08-28T04:11:32.513563+00:00, sha baac2b03f543)
  - homepage: https://flow.org/ (fetched 2026-08-29T07:55:47.710356+00:00, sha 7a8e4fe14417)
  - site_page: https://flow.org/en/docs/getting-started (fetched 2026-08-29T07:55:47.719683+00:00, sha c851d9768281)
  - site_page: https://flow.org/en/docs (fetched 2026-08-29T07:55:47.721876+00:00, sha 1a6376963469)
  - site_page: https://flow.org/en/docs/flow-vs-typescript (fetched 2026-08-29T07:55:47.723808+00:00, sha d6265bec7c16)
  - site_page: https://flow.org/en/docs/react/component-syntax (fetched 2026-08-29T07:55:47.727901+00:00, sha c67a895df9b8)
  - site_page: https://flow.org/en/docs/match (fetched 2026-08-29T07:55:47.730006+00:00, sha fae2e56a66cf)
  - site_page: https://flow.org/en/docs/types/objects (fetched 2026-08-29T07:55:47.732097+00:00, sha be1715476070)
- Data as of 2026-08-30T08:39:29.467469+00:00.