Prettier

The Prettier module keeps formatting consistent and enforced before code review. It checks formatting locally, in CI, and in Dagger Cloud, and can rewrite source to match, always using the project's own Prettier config. Each Prettier config roots a project. Keep it alongside a linter so formatting policy stays separate from lint rules.

Add it to your workspace

dagger module install dagger.io/js/prettier

Run the check

dagger check --prettier                          # check every project
dagger check --prettier-project=packages/ui      # check one project

The check is prettier/projects/format-check. It installs dependencies and runs the project's own Prettier with --check from the project directory, failing if any file isn't formatted. A check over several projects reports every project that fails.

Projects

Flag	Collection	Key
--prettier-project	projects	Directory holding the Prettier config, relative to the workspace root. The root is .

List the keys with dagger list prettier-projects -a. Select collection items describes how to select items.

A project is a directory holding .prettierrc, .prettierrc.json, .json5, .yaml, .yml, .toml, .js, .mjs, .cjs, .ts, .mts, or .cts, or prettier.config.js, .mjs, .cjs, .ts, .mts, or .cts. A config in the prettier field of package.json does not root a project. A project covers everything below it except nested projects.

Projects are found at or below the directory dagger runs from, plus the nearest project that encloses it.

The source is mounted without files ignored by .gitignore, in addition to the project's own Prettier ignore files. Dependencies install at the nearest workspace root (a pnpm-workspace.yaml or a package.json with workspaces), else the nearest lockfile, else the nearest package.json.

Fix formatting

format runs Prettier with --write and returns the reformatted source as a changeset. It is a regular function, not a check, so it doesn't run during dagger check. Call it on the project that contains a path:

dagger api call -y prettier project --path=. format

-y applies the changeset without prompting.

Configure it

List the current settings with dagger module settings prettier, then change one with dagger module settings prettier <key> <value>. They live in dagger.toml under [modules.prettier.settings] and apply to every project:

• packageManager (default empty) is the package manager that installs dependencies: npm, yarn, pnpm, or bun. Empty detects it from the packageManager field of package.json, then from the lockfile, then uses npm.
• baseImageAddress (default node:25-alpine) is the Node base image Prettier runs in. Pin it to your project's Node version, e.g. node:22-alpine.
• installFlags (default empty) are extra arguments for the install command, such as ["--ignore-scripts"].
• environment (default empty) sets environment variables for Prettier, as KEY=VALUE.

[modules.prettier.settings]
baseImageAddress = "node:22-alpine"
installFlags = ["--ignore-scripts"]

Working with other modules

Prettier pairs well with ESLint. ESLint checks code quality, Prettier owns formatting. If your project uses Biome for both, use the Biome module instead.

source code