Install nixfmt with Homebrew, Nix

Project links

• Homepage
• Upstream docs
• Package manager page

Commands and aliases

• nixfmt

Project history

The nixfmt changelog lists version 0.1.0 on May 11, 2019 as the first release and says it could parse all of nixpkgs and format it consistently, though not yet prettily in all places. The repository README later acknowledged that nixfmt was originally developed by Serokell and donated to become an official Nix project after RFC 166.

RFC 166 was merged on March 5, 2024. The RFC text on the pull request set out to define the initial standard Nix format, establish the Nix formatter team, create the official implementation, reformat Nixpkgs, and require default formatting in the Nix CLI to use the official formatter. nixfmt 1.0.0 was released on July 9, 2025 as the first stable release of the official formatter, with the changelog noting that formatting changed substantially from earlier nixfmt output.

Adoption history

nixfmt's adoption is institutional inside the Nix ecosystem rather than measured only by direct installs. The README calls it the official formatter, says the standard is defined in `standard.md`, and documents editor integration, NixOS/Home Manager installation, `nixfmt-tree`, `treefmt-nix`, direct `treefmt`, and `git-hooks.nix` workflows.

On 2026-07-01, Homebrew listed nixfmt 1.3.1 with 1,388 installs over 365 days. That undercounts its real ecosystem role because many Nix users get it from Nixpkgs and invoke it through flakes, `nix fmt`, treefmt wrappers, editor integrations, or pre-commit hooks.

How it is used

The bare CLI is simple: `nixfmt < input.nix` formats stdin to stdout, and `nixfmt file.nix` formats a file in place. The README notes that `nixfmt` itself processes one file at a time and points project-level users toward wrappers such as `nixfmt-tree`, `treefmt-nix`, `treefmt`, and `git-hooks.nix`.

For flake-based workflows, the Nix manual documents `nix fmt` as rewriting Nix files to a canonical format using the formatter specified in the flake, including examples that set the formatter to `nixfmt`. That is the package-nerd adoption path: wire nixfmt into the flake, editor, or pre-commit hook and stop arguing about style.

Why package nerds care

nixfmt matters because Nix formatting moved from preference and competing tools toward a source-backed standard with a maintained official implementation. For package databases, it is a clean example of a developer tool whose status changed through governance: Serokell project, RFC-defined standard, NixOS-org repository, then official stable formatter.

Timeline

• {'date': '2019-05-11', 'event': 'nixfmt 0.1.0 first release.'}
• {'date': '2024-03-05', 'event': 'RFC 166 merged.'}
• {'date': '2025-07-09', 'event': 'nixfmt 1.0.0 released as the first stable official formatter.'}
• {'date': '2026-07-01', 'event': 'Homebrew formula listed stable nixfmt 1.3.1.'}

Related projects

• Nix
• Nixpkgs
• nixfmt-tree
• treefmt
• treefmt-nix
• git-hooks.nix

Sources

• https://formulae.brew.sh/formula/nixfmt
• https://github.com/NixOS/nixfmt
• https://github.com/NixOS/nixfmt/blob/master/CHANGELOG.md
• https://github.com/NixOS/nixfmt/blob/master/standard.md
• https://github.com/NixOS/rfcs/pull/166
• https://nix.dev/manual/nix/2.23/command-ref/new-cli/nix3-fmt