#Configuration File

Rslint uses JS/TS module configuration with a flat config array aligned with ESLint v10.

#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 .

#Path resolution and basePath

Relative config paths normally resolve from the config entry's authored directory. Use basePath to give one entry a different starting directory. See the basePath configuration reference for its complete matching, TypeScript project, config-source, and .gitignore behavior.

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 ignores plus optional name or basePath, with no configuration fields, 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.

#Migrating a legacy JSON configuration

Rslint no longer loads rslint.json or rslint.jsonc while linting. Passing one to --config is rejected; automatic discovery ignores those filenames.

Run rslint --init in a project that still has a legacy JSON/JSONC file to migrate it to a JS/TS module config. The migration preserves custom rules and settings while deduplicating rules already covered by recommended presets.