HTTP status codes reference

Yandex publishes not just what each status code means but when to use it, and several of those recommendations differ from common practice. This is the reference to check before choosing a redirect type.

Redirects

• 301 Moved Permanently. The robot does not index the redirecting document but does index the destination. Yandex adds an instruction rarely stated elsewhere: keep the redirect active for at least six months so search engines process it correctly. Migrations where the old host is decommissioned after a month are throwing away the transfer.
• 302 Found. Temporary only — A/B tests and maintenance. If it is going to be permanent, use 301.
• 303 See Other. For redirecting a user after form submission. A page must return 200 to appear in results.
• 304 Not Modified. Yandex recommends it actively for resources that are rarely updated, frequently requested, and significant contributors to traffic — images, CSS, JavaScript. It speeds up indexing and reduces traffic.
• 305 Use Proxy. Deprecated for security reasons; do not use.
• 307 and 308. The method-preserving equivalents of 302 and 301, keeping the request method, body and original headers.
• 300 Multiple Choices. The robot cannot tell which resource the URL means; fix the headers.

Client errors worth reading carefully

• 403 Forbidden. Access denied — to have the page indexed, allow access. This is where over-aggressive bot filtering shows up.
• 404 Not Found. Yandex’s guidance is calm: if you removed a section, block it in robots.txt; if the page never existed, ignore the error — someone linked incorrectly to your site. A 404 report is not automatically a task list.
• 405 Invalid method — configure the server to support the required methods; check CORS settings.
• 406 Unacceptable — the document exists but the language or encoding is not supported by the robot.
• 401 and 402 — authentication required, and a server or payment configuration error respectively.
• 400 Bad Request — malformed request; headers and parameters must comply with the HTTP specification.

The practical point

Most sites use 301 and 302 for everything and never implement 304. That is the gap worth closing on a large site: conditional responses on static assets are one of the few crawl-efficiency levers Yandex explicitly recommends.