HTTP status code lookup

It is useful while reading logs, debugging an integration, reviewing monitoring alerts, or explaining an API response. The result is deterministic, requires no network request, and clearly marks valid but unassigned codes instead of inventing a meaning.

Read a response code without breaking your workflow

HTTP responses place a three-digit status code at the start of the protocol’s response metadata. When that code appears in a log line, webhook delivery report, browser console, reverse-proxy trace, or API client exception, this lookup provides the human-readable label immediately. Enter one integer between 100 and 599. The result repeats the normalized code, supplies its registered or commonly standardized reason phrase, and identifies the category represented by the first digit. For example, 404 resolves to “Not Found” and the client error category, while 503 resolves to “Service Unavailable” and the server error category. This is a reference lookup, not an HTTP request: it does not contact the affected site, test whether an endpoint is healthy, or infer why a particular response occurred. That separation makes the output stable and safe to use in documentation, support tools, command-line scripts, log enrichment pipelines, and educational interfaces where the code’s conventional meaning is needed without adding network latency or exposing a private URL.

Understand categories and unassigned values

The five categories come directly from the hundreds digit. Codes from 100 through 199 are informational and describe an interim response. Codes from 200 through 299 indicate success. Codes from 300 through 399 concern redirection or another step needed to complete retrieval. Codes from 400 through 499 describe a client error, meaning the request cannot be fulfilled in its current form. Codes from 500 through 599 describe a server error, meaning the server failed while handling an apparently valid request. Not every number inside those ranges has an assigned reason phrase. An in-range value such as 299 is structurally a success code, but it has no standard phrase in the lookup table, so the result says “Unassigned” while still reporting the success category. This distinction matters: rejecting every unfamiliar code would confuse a valid HTTP extension range with malformed input, while inventing a phrase would make logs and documentation misleading. Only values outside 100 through 599, fractional numbers, and nonnumeric input are treated as invalid.

Use the result correctly in debugging and automation

A reason phrase is a concise label, not a diagnosis. If an API returns 401 Unauthorized, the phrase identifies the response semantics, but the actual remedy may involve a missing bearer token, an expired session, a signature mismatch, or a policy decision described in the response body. Likewise, 500 Internal Server Error identifies a server-side failure without revealing which component failed. Use this lookup as the first interpretation step, then inspect response headers, body content, request method, retry guidance, and service-specific documentation. In automation, the category is often more durable than the phrase: a monitoring rule can group all 500–599 responses as server errors, while an interface can display the specific phrase for people. Software should still branch on the numeric code when exact behavior matters. The API costs $0.002 per request and returns small JSON fields suitable for direct storage or display. Because the calculation is local and deterministic, the same input always produces the same output and no remote system can alter the answer.