jestjs/jest · error · Error

Jest: ' ' is required for the TypeScript configuration…

Error message

Jest: '${loader}' is required for the TypeScript configuration files. Make sure it is installed
Error: ${error.message}

What it means

Thrown by registerTsLoader when the dynamic import() of the chosen loader package fails with ERR_MODULE_NOT_FOUND. The loader is named in the @jest-config-loader pragma (or defaults to 'ts-node'), but the package is not resolvable from the project. The original error is attached as {cause}.

Solutions

1. Install the named loader: npm install -D ts-node (or esbuild-register)
2. If in a monorepo, ensure the loader is resolvable from the package running Jest (add to that workspace's deps or fix hoisting)
3. Remove the @jest-config-loader pragma and rely on native Node TS support if you're on Node 22.18+/23.6+
4. Run node -e "require.resolve('ts-node')" from the project to confirm resolution

Example fix

// before: pragma set, ts-node missing
/**
 * @jest-config-loader ts-node
 */

// after: install it
// npm install -D ts-node

import * as fs from 'node:fs';
function assertLoaderInstalled(loader: 'ts-node' | 'esbuild-register'): void {
  try {
    require.resolve(loader);
  } catch {
    throw new Error(`${loader} is not installed. Run: npm install -D ${loader}`);
  }
}

async function isLoaderInstalled(loader: string): Promise<boolean> {
  try { await import(loader); return true; } catch { return false; }
}

When it happens

Trigger: Declaring @jest-config-loader ts-node without installing ts-node; running in a monorepo where the loader is hoisted to a workspace root Jest cannot resolve from; using esbuild-register without adding it to package.json.

Common situations: Fresh clones where devDependencies weren't installed (yarn install --production); monorepo hoisting differences; CI caches that dropped optional deps.

Related errors

• Jest: ' ' is not a valid TypeScript configuration loader.
• Jest: You can only define a single loader through…
• jest.config.mts requires native TypeScript support. Ensure…
• Jest: Failed to parse the TypeScript config file
• Can't find a root directory while resolving a config file…

AI-assisted analysis of jestjs/jest@8e6d128e4a (2026-08-10). Data as JSON: /api/errors/a3b224e1d4c1c2f2. Report an issue: GitHub.

Appendix: source

Thrown at packages/jest-config/src/readConfigFileAndSetRootDir.ts:240

              target: `node${process.version.slice(1)}`,
              ...extraTSLoaderOptions,
            });
          } else {
            instance?.unregister();
          }
        },
      };
    }

    throw new Error(
      `Jest: '${loader}' is not a valid TypeScript configuration loader.`,
    );
  } catch (error) {
    if (
      isError(error) &&
      (error as NodeJS.ErrnoException).code === 'ERR_MODULE_NOT_FOUND'
    ) {
      throw new Error(
        `Jest: '${loader}' is required for the TypeScript configuration files. Make sure it is installed\nError: ${error.message}`,
        {cause: error},
      );
    }

    throw error;
  }
}

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