HTTP Status Codes

Every time a browser or crawler requests a URL, the server answers with a three-digit HTTP status code. They group into families: 2xx means success (200 = OK), 3xx means redirection (301, 302), 4xx means a client-side problem (404 not found, 410 gone, 403 forbidden), and 5xx means a server-side problem (500 internal error, 503 unavailable).

Status codes are the vocabulary of technical SEO diagnostics. Crawl your site to see what each URL actually returns, and make sure it matches intent: important pages return 200, moved pages return 301, genuinely gone pages return 404 or 410, and maintenance windows return 503 (not 200 on an error page). Watch for mismatches — a "not found" page returning 200 is a soft 404; a redirect that should be permanent returning 302 delays consolidation.

Senior practitioners read status codes at scale through log files and crawl data to diagnose crawl waste and health. A rash of 5xx errors tells Google your server is unreliable and can suppress crawling; using 503 with a Retry-After during planned downtime protects your index; 410 (gone) can speed deindexing of content you deliberately removed. Fluency here separates real technical SEO from guesswork.