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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:

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.
[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