HTTP Status Code
An HTTP status code is a three-digit number a web server returns to tell a browser or search bot how it handled a request. The first digit groups codes into five classes (1xx-5xx), and in SEO these codes act as key signals that govern how search engines crawl and index a page.
- An HTTP status code is a three-digit number the server returns to report the outcome of a request, and its first digit sorts it into one of five classes (1xx through 5xx).
- Google reads status codes as crawling and indexing signals: 2xx responses move into the indexing pipeline, 4xx and 410 responses are dropped from the index, and 5xx responses temporarily slow the crawl rate.
- The codes that matter most in SEO are 200 (OK), 301 (permanent move), 302 (temporary move), 404 (not found), 410 (permanently removed), and 503 (temporarily unavailable).
- During short-lived maintenance or overload, return 503 rather than a 4xx so that indexing is preserved.
Overview
An HTTP status code is a three-digit number a web server sends along with its response to a browser or search bot. It is a standard signal that tells you at a glance whether a request succeeded, was moved elsewhere, or failed. The first digit of the code defines the nature of the response, and per MDN, codes fall into five classes ranging from 1xx through 5xx.
Status codes matter for SEO because search engines use them as direct signals for crawling and indexing decisions. For the very same page, Google handles things completely differently depending on which status code is returned: keeping the page indexed, removing it, or adjusting the crawl rate.
Status Classes
| Class | Range | Meaning |
|---|---|---|
| 1xx | 100–199 | Informational — the request is still being processed, or a protocol switch is being signaled. |
| 2xx | 200–299 | Success — the request was handled normally. |
| 3xx | 300–399 | Redirection — the request must move to another URL to complete. |
| 4xx | 400–499 | Client error — the request itself is faulty or unauthorized. |
| 5xx | 500–599 | Server error — the server failed to process a valid request. |
Key Codes for SEO
The codes below are the ones you encounter most often in SEO work. 302, 404, 410, and 503 each have their own dedicated entry where they are covered in more depth, so this section only summarizes them.
| Code | Name | Meaning and SEO handling |
|---|---|---|
| 200 | OK | Request succeeded. Google passes the content into the indexing pipeline. A 200, however, does not guarantee that the page will be indexed. |
| 301 | Moved Permanently | Permanent move. Google follows the redirect and treats it as a strong signal to process the redirect target. |
| 302 | Found | Temporary move. Google follows the redirect but treats the target as a weak signal. |
| 404 | Not Found | Resource missing. URLs that were previously indexed are dropped from search results over time. |
| 410 | Gone | Permanently removed. Handled much like 404, but it clearly states that the content has been intentionally and completely removed. |
| 503 | Service Unavailable | Temporarily down. Google briefly slows its crawl rate and preserves the index, but eventually removes the page if the error persists. |
Underlying Rationale
According to Google Search Central documentation, status codes are handled as follows. 2xx responses are passed into the indexing pipeline but do not guarantee indexing. Among 3xx responses, 301 acts as a strong signal to process the redirect target, while 302 acts as a weak one. For 4xx, 404 and 410 remove previously indexed URLs from search results and gradually halt crawling, while 429 is read as a server-overload signal that prompts the crawler to slow down.
Among 5xx responses, 503 is interpreted as a temporary problem, so Google lowers its crawl rate while prioritizing preservation of the index. Once the server returns 2xx again, Google gradually restores its crawl rate. For this reason, during temporary situations such as maintenance or overload, returning 503 rather than a 4xx is recommended: a 4xx triggers permanent removal, whereas a 503 keeps the page indexed.