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#266 in Development tools

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MIT license


treefmt - one CLI to format the code tree

Support room on Matrix

Status: beta

When working on large code trees, it's common to have multiple code formatters run against it. And have one script that loops over all of them. treefmt makes that nicer.

  • A unified CLI and output
  • Run all the formatters in parallel.
  • Cache which files have changed for super fast re-formatting.

Just type treefmt in any folder and it reformats the whole code tree.

Design decisions

We assume that the project code is checked into source control. Therefore, the default should be to write formatter changes back in place. Options like --dry-run are not needed; the source control is relied upon to revert or check for code changes.

treefmt is responsible for traversing the file-system and mapping files to specific code formatters.

Only one formatter per file. treefmt enforces that only one tool is executed per file. Guaranteeing two tools to produce idempotent outputs is quite tricky.


$ treefmt --help

treefmt 0.5.0
✨  format all your language!

    treefmt [FLAGS] [OPTIONS] [--] [paths]...

        --allow-missing-formatter    Do not exit with error if a configured formatter is missing
        --clear-cache                Reset the evaluation cache. Use in case the cache is not precise enough
        --fail-on-change             Exit with error if any changes were made. Useful for CI
    -h, --help                       Prints help information
        --init                       Create a new treefmt.toml
        --no-cache                   Ignore the evaluation cache entirely. Useful for CI
    -q, --quiet                      No output printed to stderr
        --stdin                      Format the content passed in stdin
    -V, --version                    Prints version information
    -v, --verbose                    Log verbosity is based off the number of v used

        --config-file <config-file>     Run with the specified config file, which is not required to be in the tree to
                                        be formatted
    -f, --formatters <formatters>...    Select formatters name to apply. Defaults to all formatters
        --tree-root <tree-root>         Set the path to the tree root directory. Defaults to the folder holding the
                                        treefmt.toml file [env: PRJ_ROOT=]
    -C <work-dir>                       Run as if treefmt was started in <work-dir> instead of the current working
                                        directory [default: .]

    <paths>...    Paths to format. Defaults to formatting the whole tree

Configuration format

In order to use treefmt in the project, treefmt.toml should exists in the root folder. For example, we want to use nixpkgs-fmt on our Nix project and rustfmt on our Rust project, then the treefmt.toml will be written as follows:

command = "nixpkgs-fmt"
includes = ["*.nix"]

command = "rustfmt"
options = ["--edition", "2018"]
includes = ["*.rs"]

See the wiki for more examples.

Use cases

CLI usage

As a developer, I want to run treefmt in any folder and it would automatically format all of the code, configured for the project. I don't want to remember what tool to use, or their magic incantation.

Editor integration

Editors often want to be able to format a file, before it gets written to disk.

Ideally, the editor would pipe the code in, pass the filename, and get the formatted code out. Eg: cat ./my_file.sh | treefmt --stdin my_file.sh > formatted_file.sh

CI integration

The --fail-on-change flag can be used to exit with error if any files were re-formatted.


#!/usr/bin/env bash
set -euo pipefail

# Format all of the code and exit with error if there are any changes
treefmt --fail-on-change


In order to keep the design of treefmt simple, we ask code formatters to adhere to the following specification.

treefmt formatter spec

If they don't, the best is to create a wrapper script that transforms the usage to match that spec.

  • EditorConfig: unifies file indentations configuration on a per-project basis.
  • prettier: and opinionated code formatter for a number of languages.
  • Super-Linter: a project by GitHub to lint all of the code.
  • pre-commit: a framework for managing and maintaining multi-language pre-commit hooks.


All contributions are welcome! We try to keep the project simple and focused so not everything will be accepted. Please refer to Contributing guidelines for more information.


Unless explicitly stated otherwise, any contribution intentionally submitted for inclusion in the work by you shall be licensed under the MIT license, without any additional terms or conditions.


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