yarnpkg/yarn · error · MessageError

missingWhyDependency

Error message

missingWhyDependency

What it means

Thrown at the top of 'yarn why' when no positional argument is supplied. The command needs exactly one dependency query (a package name or pattern) to explain why it is installed.

Source

Thrown at src/cli/commands/why.js:130

  commander.description('Identifies why a package has been installed, detailing which other packages depend on it.');
}

export function hasWrapper(commander: Object, args: Array<string>): boolean {
  return true;
}

// to conform to the current standard '#' as package tree separator
function toStandardPathString(pathString: string): string {
  const str = pathString.replace(/\//g, '#');
  if (str[0] === '#') {
    return str.slice(1);
  }
  return str;
}

export async function run(config: Config, reporter: Reporter, flags: Object, args: Array<string>): Promise<void> {
  if (!args.length) {
    throw new MessageError(reporter.lang('missingWhyDependency'));
  }
  if (args.length > 1) {
    throw new MessageError(reporter.lang('tooManyArguments', 1));
  }

  const query = await cleanQuery(config, args[0]);

  reporter.step(1, 4, reporter.lang('whyStart', args[0]), emoji.get('thinking_face'));

  // init
  reporter.step(2, 4, reporter.lang('whyInitGraph'), emoji.get('truck'));
  const lockfile = await Lockfile.fromDirectory(config.lockfileFolder, reporter);
  const install = new Install(flags, config, reporter, lockfile);
  const {requests: depRequests, patterns, workspaceLayout} = await install.fetchRequestFromCwd();
  await install.resolver.init(depRequests, {
    isFlat: install.flags.flat,
    isFrozen: install.flags.frozenLockfile,
    workspaceLayout,

View on GitHub (pinned to c2dda503f3)

Solutions

1. Pass a dependency name: 'yarn why <package>'.
2. You may pass a scoped name '@scope/pkg' or a path-style query.

Example fix

# before
$ yarn why
# after
$ yarn why lodash

if (!Array.isArray(args) || args.length === 0) {
  throw new Error("'yarn why' requires exactly one dependency query argument.");
}

function hasWhyQuery(args: string[]): boolean {
  return Array.isArray(args) && args.length === 1;
}

When it happens

Trigger: Running bare 'yarn why' with no arguments, so args.length is 0.

Common situations: User forgot the package name; script/alias invoked 'yarn why' without arguments.

Related errors

• invalidPackageName
• requiredVersionInRange
• tooFewArguments
• noArguments
• invalidVersionArgument

AI-assisted analysis of yarnpkg/yarn@c2dda503f3 (2026-08-13). Data as JSON: /api/errors/e5ca43904e0fb8ae. Report an issue: GitHub.