GoogleChrome/lighthouse · error

Usage $0: <url>

Error message

Usage $0: <url>

What it means

Usage guard at the top of debug-url.js, a CLI script that launches a debug Lantern run for a single URL. It reads the URL from process.argv[2] and throws immediately if no positional argument was provided. This is a standard argument-validation pattern for standalone Node scripts.

Source

Thrown at core/scripts/lantern/debug-url.js:16

#!/usr/bin/env node
/**
 * @license
 * Copyright 2018 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import path from 'path';
import {execFileSync} from 'child_process';

import constants from './constants.js';
import {LH_ROOT} from '../../../shared/root.js';
import {readJson} from '../../test/test-utils.js';

const INPUT_URL = process.argv[2];
if (!INPUT_URL) throw new Error('Usage $0: <url>');

const SITE_INDEX_PATH = path.resolve(process.cwd(), constants.SITE_INDEX_WITH_GOLDEN_PATH);
const SITE_INDEX_DIR = path.dirname(SITE_INDEX_PATH);
const RUN_ONCE_PATH = path.join(LH_ROOT, 'core/scripts/lantern/run-once.js');

const siteIndex = readJson(SITE_INDEX_PATH);
// @ts-expect-error - over-aggressive implicit any on site
const site = siteIndex.sites.find(site => site.url === INPUT_URL);
if (!site) throw new Error(`Could not find with site URL ${INPUT_URL}`);

const trace = path.join(SITE_INDEX_DIR, site.unthrottled.tracePath);
const log = path.join(SITE_INDEX_DIR, site.unthrottled.devtoolsLogPath);
process.env.LANTERN_DEBUG = 'true';
execFileSync('node', ['--inspect-brk', RUN_ONCE_PATH, trace, log], {stdio: 'inherit'});

View on GitHub (pinned to 9515cd4e58)

Solutions

1. Provide a URL as the first positional argument: `node core/scripts/lantern/debug-url.js https://example.com`
2. Ensure the URL must exactly match a site.url in the site index JSON

const INPUT_URL = process.argv[2];
if (!INPUT_URL) {
  console.error('Usage: node debug-url.js <url>');
  process.exit(1);
}

When it happens

Trigger: Running `node core/scripts/lantern/debug-url.js` with no arguments, or with arguments that don't reach argv[2] (e.g., flags parsed before the URL). process.argv[2] is undefined.

Common situations: Forgetting the URL argument. Copy-paste error in a command. Running the script through a wrapper that doesn't forward positional arguments.

Related errors

• Usage $0 <computed summary file>
• Usage $0 <expectations file>
• Invalid precomputed lantern data file
• Please provide a url
• Could not find with site URL ${INPUT_URL}

AI-assisted analysis of GoogleChrome/lighthouse@9515cd4e58 (2026-08-13). Data as JSON: /api/errors/924cbd0a4cf4d4c3. Report an issue: GitHub.