jestjs/jest · error · Error

The --config option requires a JSON string literal, or a fil

Error message

The --config option requires a JSON string literal, or a file path with one of these extensions: ${constants.JEST_CONFIG_EXT_ORDER.join(', ')}.
Example usage: jest --config ./jest.config.js

What it means

`check` throws (packages/jest-cli/src/args.ts:77) when `--config` is neither a JSON string nor a path ending in one of the recognized config extensions (.js, .ts, .mjs, .mts, .cjs, .cts, .json — see JEST_CONFIG_EXT_ORDER in jest-config/constants.ts). This stops Jest from silently treating an arbitrary file as a config.

Source

Thrown at packages/jest-cli/src/args.ts:85

    );
  }

  if (argv.ignoreProjects && argv.ignoreProjects.length === 0) {
    throw new Error(
      'The --ignoreProjects option requires the name of at least one project to be specified.\n' +
        'Example usage: jest --ignoreProjects my-first-project my-second-project',
    );
  }

  if (
    argv.config &&
    !isJSONString(argv.config) &&
    !new RegExp(
      `\\.(${constants.JEST_CONFIG_EXT_ORDER.map(e => e.slice(1)).join('|')})$`,
      'i',
    ).test(argv.config)
  ) {
    throw new Error(
      `The --config option requires a JSON string literal, or a file path with one of these extensions: ${constants.JEST_CONFIG_EXT_ORDER.join(
        ', ',
      )}.\nExample usage: jest --config ./jest.config.js`,
    );
  }

  return true;
}

export const usage =
  'Usage: $0 [--config=<pathToConfigFile>] [TestPathPatterns]';
export const docs = 'Documentation: https://jestjs.io/docs/cli';

// The default values are all set in jest-config
export const options: {[key: string]: Options} = {
  all: {
    description:
      'The opposite of `onlyChanged`. If `onlyChanged` is set by ' +

View on GitHub (pinned to f49721c78e)

Solutions

Rename/author your config with a supported extension, e.g. `jest.config.js` or `jest.config.ts`.
If you need to pass config inline, pass a JSON object string: `jest --config '{"testMatch":["**/*.test.js"]}'`.
Point `--config` at the directory containing a valid `jest.config.*` file rather than an unrelated file.

Example fix

# before
jest --config ./jest.yaml

# after
jest --config ./jest.config.js

Defensive patterns

Strategy: validation

Validate before calling

import {constants} from 'jest-config';
const CONFIG_EXT_RE = new RegExp(`\\.(${constants.JEST_CONFIG_EXT_ORDER.map(e => e.slice(1)).join('|')})$`, 'i');
function validateConfigArg(cfg?: string): void {
  if (cfg && !(cfg.trim().startsWith('{') || cfg.trim().startsWith('[')) && !CONFIG_EXT_RE.test(cfg)) {
    throw new Error(`--config must be a JSON string or a path ending in one of: ${constants.JEST_CONFIG_EXT_ORDER.join(', ')}`);
  }
}

Type guard

const isConfigPath = (s: string) => /\.(js|ts|mjs|mts|cjs|cts|json)$/i.test(s);
const isJsonString = (s: string) => s.trim().startsWith('{') || s.trim().startsWith('[');

Prevention

Prefer a jest.config.{js,ts} file over inline config.
If inlining, pass valid JSON.
Keep config in one of the supported extensions.

When it happens

Trigger: `jest --config ./config.yaml`, `jest --config jest-config.babel`, or `jest --config somefolder/` where the folder has no recognizable jest config file.

Common situations: Pointing at a YAML/TOML config (Jest has no native YAML loader), a typo in the filename, or a config written in an unsupported extension.

Related errors

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/bb00529bd69fe384.json. Report an issue: GitHub.