// Compares code formatting and formatting IR between Biome and Prettier to ensure that Biome's formatting is consistent and correct. Use when validating formatter changes, debugging formatting differences, or comparing output for JavaScript, TypeScript, CSS, or other languages.
Guide for testing workflows and code generation commands in Biome. Use when running snapshot tests for lint rules, managing insta snapshots, or regenerating analyzer/parser/formatter code after changes.
Guide for implementing parsers with error recovery for new languages in Biome. Use when adding parsing support for a new language, implementing error recovery in a parser, or writing grammar definitions in .ungram format for JavaScript, CSS, JSON, HTML, GraphQL, or other languages.
General development best practices and common gotchas when working on Biome. Use for avoiding common mistakes, understanding Biome-specific patterns (AST, syntax nodes, string extraction, embedded languages), and learning technical tips.
Step-by-step guide for creating and implementing lint rules in Biome's analyzer. Use when implementing rules like noVar, useConst, or any custom lint/assist rule, adding code actions to fix diagnostics, implementing semantic analysis for binding references, or adding configurable options to rules.
Guide for implementing ESLint-to-Biome rule option migrators inside `biome migrate eslint`. Use whenever you add or update a Biome lint rule that has an ESLint source rule with configurable options, need to deserialize plugin-specific ESLint options, or need custom migration logic beyond the auto-generated severity mapping.
Guide for implementing formatting rules using Biome's IR-based formatter infrastructure. Use when implementing formatting for new syntax nodes, handling comments in formatted output, writing or debugging formatter snapshot tests, diagnosing idempotency failures, or comparing Biome's formatting against Prettier for JavaScript, CSS, JSON, HTML, Markdown, or other languages.
| name | prettier-compare |
| description | Compares code formatting and formatting IR between Biome and Prettier to ensure that Biome's formatting is consistent and correct. Use when validating formatter changes, debugging formatting differences, or comparing output for JavaScript, TypeScript, CSS, or other languages. |
| compatibility | Designed for coding agents working on the Biome codebase (github.com/biomejs/biome). Requires bun and wasm-bindgen-cli. |
Use packages/prettier-compare/ to inspect any differences between Biome and Prettier formatting (including IR output) before shipping formatter changes.
bun (the CLI is a Bun script) and ensure dependencies have been installed.--rebuild so the Biome WASM bundle matches your current Rust changes.Snippets passed as CLI args:
bun packages/prettier-compare/bin/prettier-compare.js --rebuild 'const x={a:1,b:2}'
Force a language (useful when the tool cannot infer it from a filename):
bun packages/prettier-compare/bin/prettier-compare.js --rebuild -l ts 'const x: number = 1'
Compare files on disk:
bun packages/prettier-compare/bin/prettier-compare.js --rebuild -f src/example.tsx
Read from stdin (great for piping editor selections):
echo 'const x = 1' | bun packages/prettier-compare/bin/prettier-compare.js --rebuild -l js
-l/--language when formatting code without an extension so both formatters pick the correct parser.-f/--file for large samples or snapshot tests so you can iterate directly on project fixtures.packages/prettier-compare/README.md for deeper CLI details; mirror any updates here, keeping the hard requirement that commands include --rebuild.--rebuild since it only rebuilds the Biome WASM bundle and does not modify any source files.