@felixarntz/biome

Reusable Biome lint rules that make your agent produce better code in fewer review cycles, written as GritQL plugins. Install the package once and reference the rules from any project's Biome config — either all of them with a single line, or individually as needed — without copying .grit files around.

Rules cover aspects like type-safety escape hatches, prototype-chain-safe property access and iteration, safer dynamic-key object construction, and self-documenting function APIs.

Rules

| Rule | What it flags | | --- | --- | | no-as-unknown-as | value as unknown as T double assertions, which bypass TypeScript's type checking entirely. | | no-conditional-object-spread | Conditional object spreads such as ...(condition ? {} : { key: value }), recommending explicit object construction and property assignment. | | no-empty-object-accumulator | .reduce(..., {}) accumulator seeds, recommending Object.create(null) or Map for dynamic-key aggregation. | | no-has-own-property | Direct obj.hasOwnProperty(key) calls, recommending Object.hasOwn(obj, key) because the method can be missing or shadowed. | | no-in-operator | The in operator and for...in, recommending own-property checks and own-key iteration that do not walk the prototype chain. | | no-object-assign-target | Object.assign({}, ...) plain-object merge targets, recommending Object.assign(Object.create(null), ...). | | no-object-from-entries | Object.fromEntries(...), which creates a plain object with Object.prototype for dynamic keys. | | no-process-env-mutation | Direct writes, deletes, and Object.assign(process.env, ...) calls that mutate process-global environment state. | | no-prototype-mutation | Object.setPrototypeOf(...) and Reflect.setPrototypeOf(...), which mutate prototype chains. | | no-prototype-property-access | Direct obj.__proto__ and obj.constructor.prototype access, which are common prototype-pollution primitives. | | prefer-object-parameter | Functions, methods, and constructors with more than one positional parameter, recommending a single object argument with named parameters instead. A leading TypeScript this parameter is not counted. Inline callbacks, whose signature is dictated by the calling API, are left alone. |

Installation

pnpm add -D @felixarntz/biome @biomejs/biome

Usage

Biome plugins are enabled through the plugins array in your biome.json. Biome does not resolve plugin entries as package names — it only accepts file paths — so the rules are referenced by their path inside node_modules.

All rules at once

The package ships a generated rules/all.grit that bundles every rule. Enable the whole set with a single entry:

{
  "$schema": "https://biomejs.dev/schemas/2.4.16/schema.json",
  "plugins": ["./node_modules/@felixarntz/biome/rules/all.grit"]
}

Individual rules

Some of the rules are more opinionated than others. So if you don't want to use all of them, you can pick only the rules you want:

{
  "$schema": "https://biomejs.dev/schemas/2.4.16/schema.json",
  "plugins": [
    "./node_modules/@felixarntz/biome/rules/no-as-unknown-as.grit",
    "./node_modules/@felixarntz/biome/rules/no-conditional-object-spread.grit",
    "./node_modules/@felixarntz/biome/rules/no-empty-object-accumulator.grit",
    "./node_modules/@felixarntz/biome/rules/no-has-own-property.grit",
    "./node_modules/@felixarntz/biome/rules/no-in-operator.grit",
    "./node_modules/@felixarntz/biome/rules/no-object-assign-target.grit",
    "./node_modules/@felixarntz/biome/rules/no-object-from-entries.grit",
    "./node_modules/@felixarntz/biome/rules/no-process-env-mutation.grit",
    "./node_modules/@felixarntz/biome/rules/no-prototype-mutation.grit",
    "./node_modules/@felixarntz/biome/rules/no-prototype-property-access.grit",
    "./node_modules/@felixarntz/biome/rules/prefer-object-parameter.grit"
  ]
}

Note on the path. Plugin paths are resolved relative to the biome.json that declares them.

The ./node_modules/... form above assumes your config sits next to the node_modules that contains this package — the usual case for a single-package project, and for pnpm, whose symlink at node_modules/@felixarntz/biome resolves transparently. In a monorepo where the config and the installed package live in different directories, adjust the relative path accordingly (e.g. ../../node_modules/@felixarntz/biome/rules/all.grit).

This is a current Biome limitation: extends resolves npm packages, but plugins never does. Until Biome adds package resolution for plugins, the relative file path is the only way to reference them. Track progress in biomejs/biome discussion #6265.

Object.hasOwn type augmentation

no-in-operator and no-has-own-property steer you toward Object.hasOwn, but the built-in TypeScript signature returns a plain boolean and therefore doesn't narrow the checked object. This package ships a type augmentation that restores narrowing parity with the in operator.

Enable it by importing it once from any .ts/.d.ts file that is part of your compilation:

import "@felixarntz/biome/object-hasown";

Or reference it from tsconfig.json (requires "moduleResolution": "bundler" or "node16"):

{
  "compilerOptions": {
    "types": ["@felixarntz/biome/object-hasown"]
  }
}

After that, Object.hasOwn(obj, "key") narrows obj the same way "key" in obj would.

License

MIT