What is an HTTP Status Code?

HTTP status code: the server's answer to every request

An HTTP status code is how a web server reports what happened when a browser or crawler requested a URL. The first digit classifies the outcome:

• 1xx — informational (rare in SEO work)
• 2xx — success
• 3xx — redirection
• 4xx — client error
• 5xx — server error

Search engines use status codes to decide whether to index a URL, follow redirects, retry later, or drop a page from results. Technical SEO programs monitor status distributions at template scale—not only on the homepage.

Status codes SEO teams see most

2xx success and indexing

200 OK means the server returned a representation. Indexation still requires no noindex directives, quality thresholds, and crawlability.

Watch for:

• 200 on empty product pages (soft 404)
• 200 on infinite duplicate parameter URLs
• 200 with wrong language content

Example: sold-out product returns 200

Page shows "Product unavailable" with no alternatives—thin 200. Better: 301 to category, 404 if discontinued, or robust content explaining alternatives.

3xx redirects and signal flow

Redirects tell clients to fetch another URL.

301 / 308 — permanent

Use for:

• HTTP → HTTPS moves
• www consolidation
• Slug changes in URL structure
• Domain migrations

HTTP/1.1 301 Moved Permanently
Location: https://example.com/new-path/

Chains should be minimal: A → B, not A → B → C → D.

302 / 307 — temporary

Use for:

• Geo routing experiments
• A/B tests with short lifetimes
• Maintenance toggles

Permanent site moves should not stay on 302 for months.

Example: redirect chain waste

Old marketing links hit /promo → /2024/promo → /campaigns/promo → final 200. Consolidate to one 301 hop from /promo to final URL.

4xx client errors

404 Not Found

Broken internal linking, expired campaigns, removed products. Fix links or redirect to relevant replacements. Mass 404s after migrations signal poor site architecture planning.

410 Gone

Explicit retirement—useful for legal removals and discontinued content when deindex speed matters.

403 / 401

Public SEO pages must not require authentication. Accidental 403 to Googlebot from WAF rules blocks indexation.

Example: WAF blocks crawler

Security appliance returns 403 to Googlebot IP ranges while users see 200. Log analysis reveals bot-specific blocks—allowlist verified crawlers.

5xx server errors

Persistent 500 or 502/504 errors reduce crawl rate and trust. Google may temporarily drop URLs from index if errors continue.

503 with Retry-After

Planned maintenance can return 503 telling crawlers to retry later—prefer over fake 200 maintenance pages for brief windows.

Example: deploy regression

Release introduces PHP fatal error on /category/ templates—thousands of 500s. Organic traffic collapses within days. Roll back; fix forward with status monitoring alerts.

HTTP status codes and crawl budget

Bots retry 5xx and may deprioritize unstable hosts. Millions of 404s on discovered URLs waste crawl budget—clean sitemaps and internal linking after removals.

Status codes vs robots directives

A 404 removes the URL; noindex on 200 keeps fetch but drops index. Do not return 404 on pages you want indexed.

Measuring HTTP status codes

Sources:

• Server logs — bot vs human status histograms
• Crawl tools — per-template breakdowns
• Search Console — Page indexing, crawl stats
• Synthetic monitoring — uptime on critical URLs

Segment by user-agent: smartphone Googlebot vs desktop vs AdsBot.

HTTP status code checklist for migrations

1. Map old URLs to 301 targets (one hop)
2. Eliminate 302 placeholders on permanent moves
3. Remove migrated URLs from XML sitemap
4. Update canonical URL and internal links to 200 destinations
5. Crawl legacy URL list; zero unexpected 404/5xx on top traffic paths
6. Monitor GSC for four weeks post-cutover

Common HTTP status mistakes

Example: trailing slash split

/page returns 200, /page/ returns 404. Pick policy; 301 unify.

HTTP status code myths

• Myth: "404 passes link equity like 301." Reality: 404 drops equity; use 301 to relevant targets when moving.
• Myth: "All 3xx are equal." Reality: 301 vs 302 semantics differ for permanence.
• Myth: "Google ignores 5xx quickly." Reality: sustained errors harm crawl frequency and index stability.

How Crawlox helps with HTTP status codes

Crawlox reports status code distributions per template, maps redirect chains to final destinations, detects soft 404 patterns where 200 responses lack substantive content, and correlates bot-only 403/5xx spikes with WAF or deploy issues. Fix crawl errors and migration gaps with prioritized URL lists—before broken HTTP status code responses silently drain indexation across your catalog.