jestjs/jest · error · Error

Could not infer Prettier parser for file ${filepath}

Error message

Could not infer Prettier parser for file ${filepath}

What it means

Thrown by the prettier worker (worker.ts:42-44) when neither the resolved prettier config's `parser` field nor `prettier.getFileInfo(filepath).inferredParser` yields a parser name. Prettier formats the inline-snapshot source after the babel patcher writes it; without a parser it cannot format and Jest aborts the snapshot write.

Source

Thrown at packages/jest-snapshot/src/worker.ts:43

  ) => {
    prettier ??= require(
      /*webpackIgnore: true*/
      require.resolve(prettierPath, {
        [Symbol.for('jest-resolve-outside-vm-option')]: true,
      }),
    );

    const config = await prettier.resolveConfig(filepath, {
      editorconfig: true,
    });

    const inferredParser: string | null =
      typeof config?.parser === 'string'
        ? config.parser
        : await getInferredParser(filepath);

    if (!inferredParser) {
      throw new Error(`Could not infer Prettier parser for file ${filepath}`);
    }

    sourceFileWithSnapshots = await prettier.format(sourceFileWithSnapshots, {
      ...config,
      filepath,
      parser: inferredParser,
    });

    const {ast, text: parsedSourceFileWithSnapshots} =
      // @ts-expect-error private API
      await prettier.__debug.parse(sourceFileWithSnapshots, {
        ...config,
        filepath,
        originalText: sourceFileWithSnapshots,
        parser: inferredParser,
      });
    processPrettierAst(ast, config, snapshotMatcherNames, true);
    // Snapshots have now been inserted. Run prettier to make sure that the code is

View on GitHub (pinned to f49721c78e)

Solutions

1. Ensure the test file has a mainstream extension prettier understands (`.js`, `.ts`, `.jsx`, `.tsx`, `.mjs`, `.mts`).
2. Set `parser` explicitly in `.prettierrc` or in the `prettierPath`-resolved config for the affected files.
3. Install the prettier plugin matching the file type (e.g. `prettier-plugin-svelte`).
4. If prettier is unwanted, configure `prettierPath: null` in the Jest snapshot config to skip formatting (Jest will write unformatted inline snapshots).

Example fix

// before: jest.config.js with default prettier sniffing on an odd extension
// (test file: foo.test.mjsarb)
// after: tell prettier how to parse via .prettierrc
{ "overrides": [{ "files": "*.mjsarb", "options": { "parser": "babel" } }] }

const prettier = require('prettier');
const info = await prettier.getFileInfo(filepath);
if (!info.inferredParser && !prettierConfig.parser)
  throw new Error(`configure a prettier parser for ${filepath} or rename it`);

When it happens

Trigger: Writing/updating an inline snapshot in a test file whose extension prettier does not recognize (e.g. `.snap`, custom extension), or where the project's prettier config sets no parser and prettier's file-info heuristic returns null.

Common situations: Test files with unusual extensions (`.test.jsx.cjs` mishaps); projects without prettier installed/configured where prettier falls back to extension sniffing that fails; `.mdx`/`.vue`/`.svelte` test files without the matching prettier plugin installed; renaming test files to extensions prettier ignores.

Related errors

• Could not infer Prettier parser for file ${sourceFilePath}
• jest-snapshot: Failed to parse ${sourceFilePath}
• Jest: no snapshot insert location found
• Jest: Multiple inline snapshots for the same call are not su
• Jest: Couldn't locate all inline snapshots.

AI-assisted analysis of jestjs/jest@f49721c78e (2026-08-03). Data as JSON: /data/errors/ee429e646e267454.json. Report an issue: GitHub.