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Prettier

docs/current_docs/modules/prettier.mdx

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Prettier

Official module: dagger/prettier

Install with dagger mod install github.com/dagger/prettier.

What It Is

The Prettier module checks and rewrites formatting for files handled by Prettier.

Use it when formatting should be boring, consistent, and enforced before code review.

Use It For

  • Check formatting in CI and Dagger Cloud.
  • Generate a formatted version of the source.
  • Keep formatting policy separate from lint rules.

Main Workflows

  • check: fail when files are not formatted.
  • write: return source with Prettier formatting applied.

How to Use It

Install the module, then run its check:

bash
dagger mod install github.com/dagger/prettier

dagger check               # run every check in the workspace
dagger check prettier:check # fail when source files are not formatted

check installs dependencies and runs prettier --check . over the whole workspace using the project's own Prettier configuration, failing if any file is not formatted.

Settings

List the current settings and their values with dagger settings prettier, then set one with dagger settings prettier <key> <value>. Settings are stored in .dagger/config.toml under [modules.prettier.settings].

  • packageManager (default npm): the package manager used to install dependencies before checking. Set it to yarn or pnpm to match the project, so the same lockfile and dependency versions are used.
  • baseImageAddress (default node:25-alpine): the Node base image Prettier runs in. Pin it to the project's Node version, for example node:22-alpine.
toml
[modules.prettier.settings]
packageManager = "pnpm"
baseImageAddress = "node:22-alpine"

Rewriting files

Prettier also exposes a write function that runs prettier --write . and returns the reformatted source as a changeset. The changeset is limited to the file types Prettier owns here (.js, .ts, .jsx, .md). It is a regular function rather than a check, so it does not run during dagger check; call it with dagger function call (run dagger function list to see available functions).

Workspace Fit

Prettier works well next to ESLint: ESLint checks code quality, Prettier owns formatting. If the project uses Biome for both, use the Biome module instead.

Source

Source repo: github.com/dagger/prettier