Crawlerids

Crawlerids, commonly written as crawler IDs, are unique identifiers assigned to web crawlers to identify themselves to websites and services. They may be used to differentiate traffic from different crawlers and to facilitate access control, analytics, and policy enforcement. They can be embedded in user-agent strings, HTTP headers, or in request parameters.

In practice, some crawlers register with a directory or service and receive a persistent ID, sometimes combined with version or crawler type. A common method is an X-Crawler-ID header or including an identifier in the User-Agent, such as MyCrawler/2.1 (CrawlerID: abc123). Others rely on API keys or tokens for authenticated crawling.

Purposes include tracking crawler activity, enabling site operators to apply crawl quotas, allowlists/blocklists, and gather stats on crawl coverage. Crawler IDs also aid search engines and content aggregators in diagnosing crawl issues and distinguishing legitimate crawls from abuse.

Limitations include susceptibility to spoofing, incomplete adoption, and privacy concerns. Not all crawlers expose IDs, and some sites rely on IP-based or other heuristics. Standards for crawler IDs are not uniformly established, leading to variations in format and usage.

Related concepts include the user agent, robots.txt, robots meta tags, crawl delays, and access tokens. There is no single universal schema, but when used consistently, crawler IDs support accountability and operational control in large-scale web crawling.