n8n-io/n8n · error · Error

Unknown flag: ${arg.split('=', 1)[0]} (use --help)

Error message

Unknown flag: ${arg.split('=', 1)[0]} (use --help)

What it means

Thrown by the default case of parseArgs() (build-mcp-manifest.ts:222) when an argument starts with -- but matches no known flag case. The flag name is sanitized by splitting on '=' and taking the first segment before echoing, so any =value payload (which could contain a secret) is not leaked. The message directs the user to --help, which this CLI supports (unlike the eval CLI which has no --help).

Source

Thrown at packages/@n8n/instance-ai/evaluations/cli/build-mcp-manifest.ts:222

			case '--source': {
				const value = nextArg(argv, i, arg);
				if (value !== 'disk' && value !== 'langtracer') {
					throw new Error('--source must be "disk" or "langtracer"');
				}
				result.source = value;
				i += 2;
				break;
			}
			case '--suite':
				result.suite = nextArg(argv, i, arg);
				i += 2;
				break;
			case '-h':
			case '--help':
				return { helpRequested: true };
			default:
				if (arg.startsWith('--')) {
					throw new Error(`Unknown flag: ${arg.split('=', 1)[0]} (use --help)`);
				}
				result.slugs.push(arg);
				i += 1;
				break;
		}
	}

	if (result.iterations < 1) throw new Error('--iterations must be >= 1');
	if (result.concurrency < 1) throw new Error('--concurrency must be >= 1');
	if (result.maxAttempts < 1) throw new Error('--max-attempts must be >= 1');
	if (result.source === 'langtracer' && !result.suite) {
		throw new Error('--source langtracer requires --suite <slug>');
	}

	mkdirSync(result.outputDir, { recursive: true });
	if (!result.manifestPath) result.manifestPath = join(result.outputDir, 'manifest.json');
	if (!result.logDir) result.logDir = join(result.outputDir, 'logs');
	const base = result.manifestPath.replace(/\.json$/, '');

View on GitHub (pinned to 5ac6606e81)

Solutions

1. Run with --help to see the full flag list: iterations, concurrency, append, output-dir, manifest, log-dir, mcp-server, builder, model, max-attempts, mcp-timeout-ms, project-id, tier, workflow-dir, build-cwd, source, suite, help.
2. Correct the flag spelling or remove it.
3. Do not pass eval CLI flags (e.g. --build-via-mcp, --dataset) to this tool — they belong to eval:instance-ai.

Example fix

// before
pnpm eval:build-mcp-manifest --bulder instance-mcp
// after
pnpm eval:build-mcp-manifest --builder instance-mcp

const MANIFEST_FLAGS = new Set(['-n','--iterations','-j','--concurrency','--append','--output-dir','--manifest','--log-dir','--mcp-server','--builder','--model','--max-attempts','--mcp-timeout-ms','--project-id','--tier','--workflow-dir','--build-cwd','--source','--suite','-h','--help']);
function validateManifestFlags(args: string[]): void {
  for (const a of args) {
    if (a.startsWith('--') && !MANIFEST_FLAGS.has(a.split('=',1)[0])) {
      throw new Error(`Unknown flag: ${a.split('=',1)[0]}`);
    }
  }
}

When it happens

Trigger: Passing any unrecognized long flag to build-mcp-manifest, e.g. --iterations-mode instead of --iterations, or a flag from a different tool (e.g. eval CLI flags like --build-via-mcp, which is not valid here). The flag name is stripped of any =value before reporting.

Common situations: Typo in a flag name, using a flag from the eval CLI (which has different flags), or referencing a renamed/removed flag. The error message points to --help for the canonical list.

Related errors

• Unknown flag: ${flagName}
• Unexpected positional argument
• Invalid integer for ${flagName}
• --source must be "disk" or "langtracer"
• --iterations must be >= 1

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/116c5e4d86663323. Report an issue: GitHub.