#Configuration File

Rslint uses a flat config format (an array of config entries), aligned with ESLint v10. JS/TS configuration files are the recommended approach.

#Supported filenames

During automatic discovery, Rslint checks config files in the following order:

1. rslint.config.js
2. rslint.config.mjs
3. rslint.config.ts
4. rslint.config.mts

Automatic discovery does not consider .cjs or .cts config files. They can still be selected explicitly with --config or API overrideConfigFile.

#Config discovery

When you run rslint, it searches for a config file by walking upward from the target file or directory to the filesystem root. It uses the nearest candidate that loads successfully and falls back to an ancestor when a nearer candidate cannot be loaded.

• rslint src/foo.ts — searches from src/ upward
• rslint src/ — searches from src/ upward
• rslint (no args) — searches from the current working directory upward

In a monorepo, different files can automatically use different config files based on their location:

monorepo/
├── rslint.config.ts              ← root config
├── packages/
│   ├── foo/
│   │   ├── rslint.config.ts      ← used for files under foo/
│   │   └── src/
│   └── bar/
│       └── src/                   ← no config, inherits root

When linting from the monorepo root, Rslint automatically discovers all nested configs and applies the nearest one to each file.

#Global ignores and nested configs

For directory or no-argument lint runs, global ignores in a parent config prevent nested configs in ignored directories from contributing lint targets.

// monorepo/rslint.config.ts
export default defineConfig([
  // Global ignore — blocks directory target discovery in these directories
  { ignores: ['**/fixtures/**', 'e2e/**'] },
  js.configs.recommended,
  ts.configs.recommended,
]);

With this config, a rslint.config.ts inside e2e/ or any fixtures/ directory is not used by a root directory traversal. An explicitly named file is still resolved from its nearest config.

You can specify a config file explicitly, which overrides automatic discovery:

rslint --config path/to/rslint.config.ts .

For automatically discovered configs, relative files, ignores, and languageOptions.parserOptions.project patterns are resolved from the config file's directory.

For a config supplied with --config, those patterns are resolved from the current working directory.

To generate a default config, run:

rslint --init

#Basic configuration

A typical TypeScript project configuration:

import { defineConfig, globalIgnores, js, ts } from '@rslint/core';

export default defineConfig([
  // Files excluded from all rules
  globalIgnores(['**/dist/**', '**/fixtures/**']),
  // Presets with recommended rules
  js.configs.recommended,
  ts.configs.recommended,
  // Custom rule overrides
  {
    rules: {
      '@typescript-eslint/no-unused-vars': 'error',
      '@typescript-eslint/array-type': ['warn', { default: 'array-simple' }],
    },
  },
]);

See the Configuration overview for every available option and Rules & Presets for the available presets.

#Config merging

When multiple config entries match a file, they are merged in array order:

1. Global ignores — entries containing only ignores remove files from the target set
2. Selector union — the implicit default baseline and effective explicit files entries decide whether the config selects the file
3. Files matching — entries whose explicit files patterns don't match are skipped; entries without files cascade across the selector union
4. Entry-level ignores — matching entries do not select or configure the file, but cannot remove a target selected elsewhere
5. Rules — later entries override earlier ones; a severity-only value retains earlier options
6. Plugins — union from all matching entries
7. Settings — ordinary nested objects merge recursively; arrays and scalar values are replaced
8. Language options — ordinary nested objects merge recursively; arrays and scalar values are replaced

If no entry matches a selected file, no lint rules run for it, but the file is still parsed and included in the result so parser diagnostics remain visible. This applies to default-baseline files found during directory discovery as well as explicitly requested supported files. Global ignores remove matching targets; CLI and JavaScript API runs apply .gitignore as an additional global ignore source.

#JSON configuration (deprecated)

JSON config files (rslint.json, rslint.jsonc) are deprecated and will be removed in a future version. Run rslint --init to automatically migrate your JSON config to a JS/TS config. The migration preserves your custom rules and settings while deduplicating rules already covered by recommended presets.

The key difference is that JSON configs automatically enable all core rules and declared plugin rules as "error". JS/TS configs only enable rules explicitly declared in presets or the rules field.