# tweag/ormolu

A formatter for Haskell source code

Repository: https://github.com/tweag/ormolu
Canonical: https://ross.abutalabs.com/products/ormolu
Homepage: https://ormolu-live.tweag.io
Language: Haskell
License: NOASSERTION
License Family: other
Topics: haskell, formatter
Last push: 2026-08-24T21:03:41+00:00

## Health v2 (maintenance only)
Score: 87/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 99, release rhythm 65, longevity 100
- inputs: {"age_days": 2838, "days_push": 9, "days_rel": 79, "gap_med": 121.5, "n_releases_24m": 5}
- flags: no_license
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1072, forks 89 (observed 2026-08-28T04:03:28.426553+00:00)

## What it is
Ormolu is a formatter for Haskell source code that uses GHC's own parser and enforces a single, unconfigurable formatting style with minimal diffs and idempotent output. It ships as a CLI tool, a library, and a browser-based playground (Ormolu Live) compiled to WASM.

## Use cases
- format haskell source code
- enforce consistent haskell code style across a project
- check haskell formatting in CI
- format haskell code in the browser
- integrate haskell formatting into an editor
- reformat haskell code with minimal diffs

## When to choose
- you want one canonical Haskell style with no configuration debates
- you need a formatter that handles modern GHC language extensions reliably
- you want idempotent formatting suitable for large codebases and CI checks

## When to avoid
- you need configurable formatting options or multiple style presets
- you want a formatter for languages other than Haskell
- you prefer a style that preserves your existing whitespace choices entirely

## Facets
- artifact type: cli-tool
- maturity: active
- function: formatter, cli, parser
- domain: developer-tools, programming-languages
- platform: windows, cli, wasm
- tags: haskell, code-style, idempotent-formatting, ghc-parser, command-line, linux, macos

## Member repositories
- tweag/ormolu (main) score 87

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:03:28.426553+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 2026-08-30T06:53:44.188727+00:00, confidence not recorded.
  - readme: https://github.com/tweag/ormolu (fetched 2026-08-28T04:03:28.426553+00:00, sha 55acdbc6e055)
  - homepage: https://ormolu-live.tweag.io (fetched 2026-08-29T12:55:45.352350+00:00, sha 375f8c32e649)
- Data as of 2026-08-30T08:39:29.467469+00:00.