# TypeScript ESLint Documentation
# Source: https://raw.githubusercontent.com/typescript-eslint/typescript-eslint/main/docs/troubleshooting/typed-linting/index.mdx
# Path: docs/troubleshooting/typed-linting/index.mdx

---
id: index
title: Typed Linting
slug: /troubleshooting/typed-linting
---

import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';

## Editor ESLint reports become out-of-date after file changes

There is a known issue in at least VS Code with typed linting that files might have out-of-date lint errors after multiple updates to files on disk.
The root cause is that ESLint doesn't provide a way for editors to know about cross-file dependencies, such as type information.
This results in files receiving out-of-date type information when files they import from are changed.

You might see this as erroneous `no-unsafe-*` rule complaints on `any` or `error typed` values.
Other rules may be more subtly incorrect.

For now, the workaround is to run the _**Restart ESLint Server**_ command in VS Code (or an equivalent in other editors) when types get out of date.

See [ESLint does not re-compute cross-file information on file changes (microsoft/vscode-eslint#1774)](https://github.com/microsoft/vscode-eslint/issues/1774) for more information.

## How do I disable type-checked linting for a file?

Use [ESLint's configuration objects](https://eslint.org/docs/latest/use/configure/configuration-files#specifying-files-with-arbitrary-extensions) with our [`disable-type-checked`](../../users/Shared_Configurations.mdx#disable-type-checked) config to disable type checking for a `files` match that includes that file.

For example, to disable type-checked linting on all `.js` files:

<Tabs groupId="eslint-config">
  <TabItem value="Flat Config">

```js title="eslint.config.mjs"
import defineConfig from 'eslint/config';
import tseslint from 'typescript-eslint';

export default defineConfig(
  // ... the rest of your config ...
  {
    files: ['**/*.js'],
    extends: [tseslint.configs.disableTypeChecked],
  },
);
```

  </TabItem>
  <TabItem value="Legacy Config">

```js title=".eslintrc.cjs"
module.exports = {
  // ... the rest of your config ...
  overrides: [
    {
      extends: ['plugin:@typescript-eslint/disable-type-checked'],
      files: ['./**/*.js'],
    },
  ],
};
```

  </TabItem>
</Tabs>

Alternatively to disable type checking for files manually, you can set [`parserOptions: { project: false }`](../../packages/Parser.mdx#project) to an override for the files you wish to exclude.

## How can I disable type-aware linting for a set of files?

You can combine ESLint's [overrides](https://eslint.org/docs/latest/use/configure/configuration-files#configuration-based-on-glob-patterns) config in conjunction with our [`disable-type-checked`](../../users/Shared_Configurations.mdx#disable-type-checked) config to turn off type-aware linting on specific subsets of files.

<Tabs groupId="eslint-config">
<TabItem value="Flat Config">

```js title="eslint.config.mjs"
export default defineConfig(
  eslint.configs.recommended,
  tseslint.configs.recommendedTypeChecked,
  tseslint.configs.stylisticTypeChecked,
  {
    languageOptions: {
      parserOptions: {
        projectService: true,
      },
    },
  },
  // Added lines start
  {
    files: ['**/*.js'],
    extends: [tseslint.configs.disableTypeChecked],
  },
  // Added lines end
);
```

</TabItem>
<TabItem value="Legacy Config">

```js title=".eslintrc.js"
module.exports = {
  extends: [
    'eslint:recommended',
    'plugin:@typescript-eslint/recommended-type-checked',
    'plugin:@typescript-eslint/stylistic-type-checked',
  ],
  plugins: ['@typescript-eslint'],
  parser: '@typescript-eslint/parser',
  parserOptions: {
    projectService: true,
    tsconfigRootDir: __dirname,
  },
  root: true,
  // Added lines start
  overrides: [
    {
      files: ['*.js'],
      extends: ['plugin:@typescript-eslint/disable-type-checked'],
    },
  ],
  // Added lines end
};
```

</TabItem>
</Tabs>

:::info
If you use type-aware rules from other plugins, you will need to manually disable these rules or use a premade config they provide to disable them.
:::

## typescript-eslint thinks my variable is never nullish / is `any` / etc., but that is clearly not the case to me

Our type-aware rules almost always trust the type information provided by the TypeScript compiler. Therefore, an easy way to check if our rule is behaving correctly is to inspect the type of the variable in question, such as by hovering over it in your IDE.

If the IDE also shows that the type is never nullish / is `any`, you need to fix the type. A very common case is with the [`no-unnecessary-condition`](/rules/no-unnecessary-condition) rule. Take this code for example:

```ts
let condition = false;

const f = () => (condition = true);
f();

if (condition) {
  //^^^^^^^^^ Unnecessary conditional, value is always falsy.
}
```

You can see that the type of `condition` is actually the literal type `false` by hovering over it in your IDE. In this case, typescript-eslint cannot possibly know better than TypeScript itself, so you need to fix the report by fixing the type, such as through an assertion (`let condition = false as boolean`).

If the IDE provides different type information from typescript-eslint's report, then make sure that the TypeScript setup used for your IDE, typescript-eslint, and `tsc` are the same: the same TypeScript version, the same type-checking compiler options, and the same files being included in the project. For example, if a type is declared in another file but that file is not included, the type will become `any`, and cause our `no-unsafe-*` rules to report.

## Are TypeScript project references supported?

Yes, but only with [`parserOptions.projectService`](../../packages/Parser.mdx#projectservice).

See [issue #2094 discussing project references](https://github.com/typescript-eslint/typescript-eslint/issues/2094) for more details.

## Project Service Issues

[`parserOptions.projectService`](../../packages/Parser.mdx#projectservice) is the recommended parser option to enable typed linting as of typescript-eslint v8.
It enforces projects generate type information for typed linting from the same `tsconfig.json` files used by editors such as VS Code.

### I get errors telling me "... was not found by the project service. Consider either including it in the tsconfig.json or including it in allowDefaultProject"

These errors are caused by attempting to use the project service to lint a file not explicitly included in its nearest `tsconfig.json`.

The project service will attempt to build type information for each file being linted using the nearest `tsconfig.json` on disk to that file.
If that `tsconfig.json` does not include the file, and the file isn't allowlisted in [`allowDefaultProject`](../../packages/parser#allowdefaultproject), then the project service will throw this error.

For each file being reported:

- If you **do not** want to lint the file:
  - Use [one of the options ESLint offers to ignore files](https://eslint.org/docs/latest/user-guide/configuring/ignoring-code), such an `ignores` config key.
- If you **do** want to lint the file:
  - If you **do not** want to lint the file with [type-aware linting](../../getting-started/Typed_Linting.mdx): [disable type-checked linting for that file](#how-do-i-disable-type-checked-linting-for-a-file).
  - If you **do** want to lint the file with [type-aware linting](../../getting-started/Typed_Linting.mdx):
    1. If possible, add the file to the closest `tsconfig.json`'s `include`. For example, allowing `.js` files:
       ```diff title="tsconfig.json"
       "include": [
         "src",
       + "*.js"
       ]
       ```
    2. Otherwise, if you have a small number of "out of project" files, try setting [`projectService.allowDefaultProject`](../../packages/parser#allowdefaultproject).
    3. If not, you can switch to [`parserOptions.project`](../../packages/Parser.mdx#project) for more fine-grained control of projects.

Note also:

- TSConfigs don't include `.js` files by default.
  Enabling [`allowJs`](https://www.typescriptlang.org/tsconfig/#allowJs) or [`checkJs`](https://www.typescriptlang.org/tsconfig/#checkJs) is required to do so.
- The project service _only_ looks at `tsconfig.json` files.
  It does not look at `tsconfig.eslint.json` or other coincidentally-similarly-named files.

If these steps don't work for you, please [file an issue on typescript-eslint's typescript-estree package](https://github.com/typescript-eslint/typescript-eslint/issues/new?assignees=&labels=enhancement%2Ctriage&projects=&template=07-enhancement-other.yaml&title=Enhancement%3A+%3Ca+short+description+of+my+proposal%3E) telling us your use case and why you need more out-of-project files linted.
Be sure to include a minimal reproduction we can work with to understand your use case!

<HiddenHeading id="allowdefaultproject-glob-too-wide" />

### I get errors telling me "Having many files run with the default project is known to cause performance issues and slow down linting."

These errors are caused by attempting to use the project service to lint too many files not explicitly included in a `tsconfig.json` with its [`allowDefaultProject`](../../packages/parser#allowdefaultproject) option.

typescript-eslint allows up to 8 "out of project" files by default.
Each file causes a new TypeScript "program" to be built for each file it includes, which incurs a performance overhead _for each file_.

For each file being reported:

- If you **do not** want to lint the file:
  - Use [one of the options ESLint offers to ignore files](https://eslint.org/docs/latest/user-guide/configuring/ignoring-code), such an `ignores` config key.
- If you **do** want to lint the file:
  - If you **do not** want to lint the file with [type-aware linting](../../getting-started/Typed_Linting.mdx): [disable type-checked linting for that file](#how-do-i-disable-type-checked-linting-for-a-file).
  - If you **do** want to lint the file with [type-aware linting](../../getting-started/Typed_Linting.mdx):
    1. If possible, add the file to the closest `tsconfig.json`'s `include` instead of adding it to `allowDefaultProject`. For example, allowing `.js` files:
       ```diff title="tsconfig.json"
       "include": [
         "src",
       + "*.js"
       ]
       ```
    2. If not, you can switch to [`parserOptions.project`](../../packages/Parser.mdx#project) for more fine-grained control of projects.

### I'd like to use TSConfigs other than `tsconfig.json`s for project service type information

Only the TSConfig path used for "out of project" files in [`allowDefaultProject`](../../packages/Parser.mdx#allowdefaultproject) can be customized.
Otherwise, only `tsconfig.json` files on disk will be read.

For example, instead of:

- `tsconfig.json`s for building (and, coincidentally, type information in editors)
- Separate TSConfig(s) like `tsconfig.eslint.json` for linting

Consider using:

- `tsconfig.json`s for linting (and, intentionally, the same type information in editors)
- Separate TSConfig(s) like `tsconfig.build.json` for building

The project service uses the same underlying TypeScript logic as editors such as VS Code.
Using only `tsconfig.json` for typed linting enforces that the types seen in your editor match what's used for linting.

## Traditional Project Issues

### I get errors telling me "ESLint was configured to run ... However, that TSConfig does not / none of those TSConfigs include this file"

These errors are caused by an ESLint config requesting type information be generated for a file that isn't included in the TypeScript configuration.

#### Fixing the Error

- If you **do not** want to lint the file:
  - Use [one of the options ESLint offers to ignore files](https://eslint.org/docs/latest/user-guide/configuring/ignoring-code), namely a `.eslintignore` file, or `ignorePatterns` config.
- If you **do** want to lint the file:
  - If you **do not** want to lint the file with [type-aware linting](../../getting-started/Typed_Linting.mdx):
    - Use [ESLint's configuration objects](https://eslint.org/docs/latest/use/configure/configuration-files#specifying-files-with-arbitrary-extensions) with our [`disable-type-checked`](../../users/Shared_Configurations.mdx#disable-type-checked) config to disable type checking for just that type of file.
  - If you **do** want to lint the file with [type-aware linting](../../getting-started/Typed_Linting.mdx):
    - Check the `include` option of each of the TSConfigs that you provide to `parserOptions.project` - you must ensure that all files match an `include` glob, or else our tooling will not be able to find it.
      - If the file is a `.cjs`, `.js`, or `.mjs` file, make sure [`allowJs`](https://www.typescriptlang.org/tsconfig#allowJs) is enabled.
    - If your file shouldn't be a part of one of your existing tsconfigs (for example, it is a script/tool local to the repo), then consider creating a new tsconfig (we advise calling it `tsconfig.eslint.json`) in your project root which lists this file in its `include`. For an example of this, you can check out the configuration we previously used in this repo:
      - [`tsconfig.eslint.json`](https://github.com/typescript-eslint/typescript-eslint/blob/958fecaef10a26792dc00e936e98cb19fd26d05f/tsconfig.eslint.json)
      - [`eslint.config.mjs`](https://github.com/typescript-eslint/typescript-eslint/blob/958fecaef10a26792dc00e936e98cb19fd26d05f/.eslintrc.js)

#### More Details

This error may appear from the combination of two things:

- The ESLint configuration for the source file specifies at least one TSConfig file in `parserOptions.project`
- None of those TSConfig files includes the source file being linted
  - Note that files with the same name and different extension may not be recognized by TypeScript: see [`parserOptions.project` docs](../../packages/parser/#project)

When TSConfig files are specified for parsing a source file, `@typescript-eslint/parser` will use the first TSConfig that is able to include that source file (per [aka.ms/tsconfig#include](https://www.typescriptlang.org/tsconfig#include)) to generate type information.
However, if no specified TSConfig includes the source file, the parser won't be able to generate type information.

This error most commonly happens on config files or similar that are not included in their project TSConfig(s).
For example, many projects have files like:

- An `.eslintrc.cjs` / `eslint.config.mjs` with `parserOptions.project: true`
- A `tsconfig.json` with `include: ["src"]`

In that case, viewing the file in an IDE with the ESLint extension will show the error notice that the file couldn't be linted because it isn't included in `tsconfig.json`.

See our docs on [type aware linting](../../getting-started/Typed_Linting.mdx) for more information.

### I get errors telling me "The file must be included in at least one of the projects provided"

You're using an outdated version of `@typescript-eslint/parser`.
Update to the latest version to see a more informative version of this error message, explained [above](#i-get-errors-telling-me-eslint-was-configured-to-run--however-that-tsconfig-does-not--none-of-those-tsconfigs-include-this-file 'backlink to I get errors telling me ESLint was configured to run ...').

### Can I customize the TSConfig used for the project?

Yes, but it's not recommended in most configurations.
`parserOptions.projectService` uses the same "project service" APIs used by editors such as VS Code to generate TypeScript's type information.
Using a different TSConfig runs the risk of providing different types for typed linting than what your editor or `tsc` see.

If you absolutely must, the `parserOptions.project` option can be used instead of `parserOptions.projectService` with either:

- `true`: to always use `tsconfig.json`s nearest to source files
- `string | string[]`: any number of glob paths to match TSConfig files relative to `parserOptions.tsconfigRootDir`, or the current working directory if that is not provided

For example, if you use a specific `tsconfig.eslint.json` for linting, you'd specify:

<Tabs groupId="eslint-config">
<TabItem value="Flat Config">

```js title="eslint.config.mjs"
export default defineConfig({
  // ...
  languageOptions: {
    parserOptions: {
      project: './tsconfig.eslint.json',
    },
  },
  // ...
});
```

</TabItem>
<TabItem value="Legacy Config">

```js title=".eslintrc.js"
module.exports = {
  // ...
  parserOptions: {
    project: './tsconfig.eslint.json',
    tsconfigRootDir: __dirname,
  },
  // ...
};
```

</TabItem>
</Tabs>

See [the `@typescript-eslint/parser` `project` docs for more details](../../packages/Parser.mdx#project).

:::note
If your project is a multi-package monorepo, see [Troubleshooting > Typed Linting > Monorepos](./Monorepos.mdx).
:::