yarnpkg/yarn · error · MessageError

Error parsing JSON at $0, $1.

Error message

Error parsing JSON at $0, $1.

What it means

Thrown by `readJson` when the underlying factory (default `fs.readJson`, or `fs.readJsonAndFile`) throws a `SyntaxError`. Yarn catches it and rethrows as a `MessageError` (`jsonError`) with the file path (`$0`) and the original parse message (`$1`) so the user knows exactly which JSON file is malformed.

Source

Thrown at src/config.js:970

          object[field] = sortObject(object[field]);
        }
      }

      await fs.writeFilePreservingEol(loc, JSON.stringify(object, null, indent || constants.DEFAULT_INDENT) + '\n');
    }
  }

  /**
   * Call the passed factory (defaults to fs.readJson) and rethrow a pretty error message if it was the result
   * of a syntax error.
   */

  readJson(loc: string, factory: (filename: string) => Promise<Object> = fs.readJson): Promise<Object> {
    try {
      return factory(loc);
    } catch (err) {
      if (err instanceof SyntaxError) {
        throw new MessageError(this.reporter.lang('jsonError', loc, err.message));
      } else {
        throw err;
      }
    }
  }

  static async create(opts: ConfigOptions = {}, reporter: Reporter = new NoopReporter()): Promise<Config> {
    const config = new Config(reporter);
    await config.init(opts);
    return config;
  }
}

export function extractWorkspaces(manifest: ?Manifest): ?WorkspacesConfig {
  if (!manifest || !manifest.workspaces) {
    return undefined;
  }

View on GitHub (pinned to c2dda503f3)

Solutions

1. Open the file path reported in `$0` and fix the JSON syntax error described in `$1`.
2. Validate with a JSON linter: `node -e "JSON.parse(require('fs').readFileSync('<file>'))"`.
3. If it is a cache metadata file, run `yarn cache clean`.
4. Resolve git merge-conflict markers in the file before running Yarn.

Example fix

// before (package.json — trailing comma)
{
  "name": "app",
  "version": "1.0.0",
}
// after
{
  "name": "app",
  "version": "1.0.0"
}

const fs = require('fs');
function validateJsonFile(filePath) {
  try {
    JSON.parse(fs.readFileSync(filePath, 'utf8'));
    return true;
  } catch (err) {
    console.error(`Invalid JSON in ${filePath}: ${err.message}`);
    return false;
  }
}
// validate package.json before running yarn
validateJsonFile('package.json');

function isParsableJson(text) {
  try { JSON.parse(text); return true; } catch { return false; }
}

try {
  return await config.readJson(loc, factory);
} catch (err) {
  if (err instanceof MessageError && err.message.startsWith('Error parsing JSON')) {
    reporter.error(`Fix JSON syntax in ${loc}, then re-run.`);
    throw err;
  }
  throw err;
}

When it happens

Trigger: Any JSON file Yarn reads is malformed: package.json with a trailing comma or comment, .yarnrc.json, yarn-metadata.json in the cache, or a registry response written to disk. Reached during `readJson` calls in config, manifest reading, and lockfile JSON operations.

Common situations: Hand-editing package.json and leaving a syntax error (unquoted key, trailing comma). A JSON5-style comment accidentally saved into package.json. Corrupted cache metadata after a crash. Merge-conflict markers left in package.json.

Related errors

• unknownPackageName
• unknownPackageName
• workspaceRootNotFound
• workspaceRootNotFound
• The workspaces field in package.json must be an array.

AI-assisted analysis of yarnpkg/yarn@c2dda503f3 (2026-08-13). Data as JSON: /api/errors/b11eb2fd397ea5c7. Report an issue: GitHub.