biome-js

SKILL.md

BiomeJS Skill

Quick guidance for BiomeJS configuration based on Sablier project patterns.

Core Concepts

Extending Shared Configs

Extend shared configs via npm package exports. The consuming project must always provide its own files.includes:

{
  "$schema": "./node_modules/@biomejs/biome/configuration_schema.json",
  "extends": ["@sablier/devkit/biome"],
  "files": {
    "includes": ["**/*.{js,json,jsonc,ts}", "!node_modules/**/*"]
  }
}

For UI projects, extend both base and ui configs:

{
  "extends": ["@sablier/devkit/biome/base", "@sablier/devkit/biome/ui"],
  "files": {
    "includes": ["**/*.{css,js,jsx,json,jsonc,ts,tsx}"]
  }
}

Monorepo Inheritance

In monorepos, workspace configs inherit from root using "//":

// packages/my-package/biome.jsonc
{
  "extends": ["//"],
  "overrides": [
    // package-specific overrides
  ]
}

File Includes Pattern

Always specify files.includes explicitly. Common patterns:

Project Type
Pattern

Library
**/*.{js,json,jsonc,ts}

UI/Frontend
**/*.{css,js,jsx,json,jsonc,ts,tsx}

With GraphQL
**/*.{css,graphql,js,jsx,json,jsonc,ts,tsx}

Exclusions: !node_modules/**/*, !**/generated, !dist

Common Overrides

Test Files

Relax strict rules in test files:

{
  "overrides": [
    {
      "includes": ["**/tests/**/*.ts", "**/*.test.ts"],
      "linter": {
        "rules": {
          "style": {
            "noNonNullAssertion": "off"
          },
          "suspicious": {
            "noExplicitAny": "off"
          }
        }
      }
    }
  ]
}

Generated/ABI Files

Disable sorting and compact formatting for generated code:

{
  "overrides": [
    {
      "includes": ["**/abi/**/*.ts", "**/generated/**/*.ts"],
      "assist": {
        "actions": {
          "source": {
            "useSortedKeys": "off"
          }
        }
      },
      "javascript": {
        "formatter": {
          "expand": "never"
        }
      }
    }
  ]
}

Import Restrictions

Enforce barrel imports for specific modules:

{
  "overrides": [
    {
      "includes": ["src/**/*.{ts,tsx}"],
      "linter": {
        "rules": {
          "correctness": {
            "noRestrictedImports": {
              "level": "error",
              "options": {
                "paths": {
                  "@/core": "Import from @/core (barrel) instead of subpaths"
                }
              }
            }
          }
        }
      }
    }
  ]
}

Key Rules Reference

Rule
Default
Rationale

noFloatingPromises
error
Floating promises cause bugs

noUnusedImports
off
Allow during dev, enforce in pre-commit

noUnusedVariables
error
Keep code clean

useImportType
warn (separatedType)
Explicit type imports

useSortedKeys
on
Consistent object ordering

useSortedClasses
warn (UI)
Tailwind class sorting

useFilenamingConvention
kebab/camel/Pascal
Flexible naming

noVoid
off
Useful for useEffect callbacks

useTemplate
off
Allow string concatenation

Git Hooks Integration

Lint-Staged Configuration

Standard pattern for pre-commit hooks:

// .lintstagedrc.js
module.exports = {
  "*.{json,jsonc,ts,tsx}": "bun biome check --write",
  "*.{md,yml,yaml}": "bun prettier --cache --write",
  "*.{ts,tsx}": "bun biome check --write --only=correctness/noUnusedImports",
};

The separate noUnusedImports pass enforces import cleanup only at commit time, not during development.

UI-Specific Configuration

For frontend projects with Tailwind CSS:

{
  "css": {
    "parser": {
      "tailwindDirectives": true
    }
  },
  "assist": {
    "actions": {
      "source": {
        "useSortedAttributes": "on"
      }
    }
  },
  "linter": {
    "rules": {
      "nursery": {
        "useSortedClasses": {
          "fix": "safe",
          "level": "warn",
          "options": {
            "attributes": ["classList"],
            "functions": ["clsx", "cva", "cn", "tv", "tw"]
          }
        }
      }
    }
  }
}

Biome v2.4.0+ auto-enables CSS Modules parsing for *.module.css, so explicit
"cssModules": true is usually unnecessary unless your project needs non-standard behavior.

Biome v2.4+ Notes

biome check and biome ci now support --only and --skip for targeted rule/action runs.

biome check --write now also applies formatting when applying fixes.

Config lookup now also supports hidden files: .biome.json and .biome.jsonc.

Config lookup now also supports user config directories (for example, $HOME/.config/biome on Linux/macOS equivalents).

New formatter option formatter.trailingNewline can disable trailing newline insertion.

HTML formatter behavior changed significantly in v2.4.0; expect larger diffs in HTML/Vue/Svelte/Astro if formatter support is enabled.

Troubleshooting

Common Issues

"No files matched": Check files.includes patterns match your file structure.

Conflicting rules: Overrides are applied in order; later overrides take precedence.

Schema errors: Use local schema reference for IDE support:

"$schema": "./node_modules/@biomejs/biome/configuration_schema.json"

Biome vs Prettier

Biome handles JS/TS/JSON/CSS formatting. Use Prettier for:

Markdown (.md, .mdx)

YAML (.yml, .yaml)

Additional Resources

Examples

Working examples in ./examples/:

./examples/base-config.jsonc - Minimal library configuration

./examples/ui-config.jsonc - Frontend project with Tailwind

./examples/lint-staged.js - Pre-commit hook configuration

Full Documentation

For advanced features, migrations, or complete rule reference, consult the official Biome documentation via Context7 MCP:

Use context7 to fetch Biome documentation for [specific topic]

The official docs at biomejs.dev should be consulted as a last resort for features not covered here.