Code Formatter

Overview

Formats and validates code files using Prettier and related formatting tools. Supports JavaScript, TypeScript, JSON, CSS, Markdown, and many other file types.

Prerequisites

Node.js (v16+) and npm/npx installed
Prettier available globally (npm install -g prettier) or locally in the project
Write permissions for target files and configuration directories
Supported file types present in the project (.js, .jsx, .ts, .tsx, .json, .css, .md)

Instructions

Check whether Prettier is available by running npx prettier --version. If missing, install it locally with npm install --save-dev prettier or globally with npm install -g prettier.
Detect existing configuration by searching for .prettierrc, .prettierrc.json, prettier.config.js, or a "prettier" key in package.json. If no configuration exists, create a .prettierrc with sensible defaults (see ${CLAUDE_SKILL_DIR}/references/implementation.md).
Run npx prettier --check "**/*.{js,jsx,ts,tsx,json,css,md}" --ignore-path .prettierignore to identify files that need formatting. Report the count and list of non-conforming files.
Apply formatting to identified files using npx prettier --write on the target paths. For single files, specify the exact path; for directories, use glob patterns.
Create or update .prettierignore to exclude generated outputs (dist/, build/, *.min.js, *.min.css), dependencies (node_modules/, vendor/), and lock files.
Optionally set up pre-commit enforcement by installing husky and lint-staged, then configuring lint-staged in package.json to run prettier --write on staged files matching supported extensions.
Run a final npx prettier --check to confirm all target files now conform to the configured style rules.

Output

A formatting execution report containing:

Count of files checked and files reformatted
List of files that were modified with before/after formatting status
Configuration file(s) created or updated (.prettierrc, .prettierignore)
Any git hook integration changes applied
Confirmation of final formatting compliance

Error Handling

Error	Cause	Solution
`prettier: command not found`	Prettier not installed globally or locally	Run `npm install -g prettier` or `npx prettier --version` to use npx
Syntax errors in source files	Malformed code that Prettier cannot parse	Fix syntax errors first using `npx eslint --fix-dry-run <file>` then retry formatting
Configuration conflicts	Multiple `.prettierrc` files or conflicting `editorconfig`	Locate all config files with `find . -name ".prettier*"` and consolidate to a single config
Permission denied on write	File or directory lacks write permission	Run `chmod u+w <file>` to grant write access
Parser not found for file type	Unsupported file extension or missing Prettier plugin	Install the appropriate Prettier plugin (e.g., `prettier-plugin-svelte`) or exclude the file type

Examples

Format a single file: Trigger: "Format src/app.js" Process: Run npx prettier --write src/app.js. Report the file as reformatted or already conformant.

Project-wide formatting setup: Trigger: "Set up code formatting for this project." Process: Create .prettierrc with project defaults, create .prettierignore excluding build outputs, run npx prettier --write "src/**/*.{js,ts,json,css}", install husky and lint-staged for pre-commit hooks, verify compliance.

Check formatting without modifying files: Trigger: "Check formatting across the project." Process: Run npx prettier --check "**/*.{js,jsx,ts,tsx,json,css,md}". Report non-conforming files with their paths. Suggest npx prettier --write to fix.

Resources

${CLAUDE_SKILL_DIR}/references/implementation.md -- detailed implementation guide with configuration examples
${CLAUDE_SKILL_DIR}/references/errors.md -- common error scenarios and solutions
Prettier documentation -- official configuration and CLI reference
ESLint -- complementary linting and code quality tool
Husky -- git hooks for pre-commit formatting enforcement

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