noUnusedLocals and noUnusedParameters

noUnusedLocals reports local variables, functions and imports that are declared but never read; noUnusedParameters does the same for function parameters. Both use TS6133 ("is declared but its value is never read"). Exported names are not local, so they are never reported.

Neither is part of strict. Both arrived with TypeScript 2.0.

At a glance

Write	Optional. Many projects leave both off and let a linter report unused names as warnings
On the command line	`--noUnusedLocals`
Type	boolean
Default in TypeScript 5.9	`false`
TypeScript's description	Enable error reporting when local variables aren't read.

The description is quoted from TypeScript's own option list (Apache-2.0); see the notices.

Examples

main.js Error confirmed 5.9.3 TypeScript 5.9.3, run 21 October 2026: main.js(2,1): error TS6133: 'readFile' is declared but its value is never read. main.js(10,29): error TS6133: 'retries' is declared but its value is never read. main.js(12,9): error TS6133: 'prefix' is declared but its value is never read. 6.0.3 TypeScript 6.0.3, run 21 October 2026: the same as 5.9.3. main.js(2,1): error TS6133: 'readFile' is declared but its value is never read. main.js(10,29): error TS6133: 'retries' is declared but its value is never read. main.js(12,9): error TS6133: 'prefix' is declared but its value is never read. 7.0.2 TypeScript 7.0.2, run 21 October 2026: the same as 5.9.3. main.js(2,10): error TS6133: 'readFile' is declared but its value is never read. main.js(10,29): error TS6133: 'retries' is declared but its value is never read. main.js(12,9): error TS6133: 'prefix' is declared but its value is never read. checked 21 October 2026

import { readFile } from "node:fs/promises";error TS6133: 'readFile' is declared but its value is never read.

/**
 * @param {string} name
 * @param {number} retries
 * @param {unknown} _context
 */
export function greet(name, retries, _context) {error TS6133: 'retries' is declared but its value is never read.
  const prefix = "Hello";error TS6133: 'prefix' is declared but its value is never read.
  return `Hi, ${name}`;
}

noUnusedLocals and noUnusedParameters on.

jsconfig.json for this example

{
  "compilerOptions": {
    "checkJs": true,
    "noEmit": true,
    "strict": true,
    "target": "es2022",
    "module": "nodenext",
    "types": [
      "node"
    ],
    "noUnusedLocals": true,
    "noUnusedParameters": true
  },
  "include": [
    "*.js"
  ]
}

main.js TypeScript 5.9.3 TypeScript 5.9.3, run 21 October 2026: No errors. 6.0.3 TypeScript 6.0.3, run 21 October 2026: the same as 5.9.3. No errors. 7.0.2 TypeScript 7.0.2, run 21 October 2026: the same as 5.9.3. No errors. checked 21 October 2026

import { readFile } from "node:fs/promises";

/**
 * @param {string} name
 * @param {number} retries
 * @param {unknown} _context
 */
export function greet(name, retries, _context) {
  const prefix = "Hello";
  return `Hi, ${name}`;
}

Both off: unused names pass.

jsconfig.json for this example

{
  "compilerOptions": {
    "checkJs": true,
    "noEmit": true,
    "strict": true,
    "target": "es2022",
    "module": "nodenext",
    "types": [
      "node"
    ]
  },
  "include": [
    "*.js"
  ]
}

Keeping a parameter you do not use

A callback often has to accept a parameter it ignores. Start its name with an underscore, as _context does in the example, and noUnusedParameters leaves it alone.

Errors, not warnings

TypeScript reports these as errors, so npm run lint fails while you are halfway through a change and a variable is not used yet. That is why many teams leave both off and use a linter rule instead, which can be a warning. Bun's recommended config, for example, sets both to false.

Gotchas

An import used only in a JSDoc type counts as used.

Sources

TSConfig Reference: noUnusedLocals · TypeScript
TSConfig Reference: noUnusedParameters · TypeScript
TypeScript 2.0 release notes · TypeScript handbook
TypeScript 2.6 release notes · TypeScript handbook
TypeScript · Bun docs

Last reviewed 20 October 2026.

noUnusedLocals and noUnusedParameters

At a glance

Examples

Keeping a parameter you do not use

Errors, not warnings

Gotchas

Related pages

strict

@import

TS6133: A variable, import or parameter that is never read

Sources