Ormolu review
A focused GHC-based formatter for consistent Haskell code and CI checks.
Reviewed by iTechGuides Editors · Editorial team · Updated Oct 2026
Ormolu is an open-source code formatter for Haskell source code, aimed at teams and individual developers who want a consistent style built around GHC’s parser. It can print formatted code to standard output, replace files in place, check whether files are formatted, process multiple files, and format selected regions by line range. Its focus is narrow and clear: Haskell formatting across Linux, macOS, Windows, and the web.
The strongest part of Ormolu is its Haskell-specific parsing and language coverage. It supports language extensions, dependencies, fixities, and re-exports, while magic comments can disable or enable formatting in selected areas. The stated formatting approach is designed for minimal diffs and idempotent output, which suits teams that want predictable changes in code review. A stable library module also lets Haskell programs use Ormolu as a library rather than only as a command-line tool.
Ormolu fits existing development workflows through Emacs, VS Code, Vim, Haskell Language Server, and GitHub Actions integrations. Configuration can be provided through .ormolu files, and the formatting check mode is suited to CI enforcement. The trade-off is its deliberately limited language scope: teams working across several programming languages will need another formatter for the rest of their codebase. It also has no AI features. Choose Ormolu when Haskell and GHC-based parsing are the priority; choose an alternative when you need a multi-language formatter or broader automated coding features.
Ormolu pros and cons
- Where it wins
- Uses GHC’s parser and supports Haskell language extensions
- Formats, checks, or replaces files from the command line
- Integrates with editors, Haskell Language Server, and GitHub Actions
- Where it doesn't
- Supports Haskell rather than multiple programming languages
- Does not include AI features
- Its formatting scope is centered on source code rather than broader workflows
Ormolu fact sheet, pricing and score →
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