An HTTP status code is a three-digit integer from 100 through 599. Its first digit defines the response class: 1xx informational, 2xx successful, 3xx redirection, 4xx client error, and 5xx server error. This lookup reports the class and the standard reason phrase for its built-in IANA-derived assignments.
Class-valid does not mean assigned. A code such as 599 fits the server-error class but may be unassigned by IANA or defined only by a proxy, framework, or private protocol. tryb labels that distinction instead of inventing a universal meaning for every number in the range.
The reason phrase is explanatory text, not a complete diagnosis. A 404 means the server did not find a current representation for the target resource in that response context; it does not by itself prove that the route never existed, that a deployment is broken, or which component generated the response.
Edge cases worth knowing
- Unassigned codes
- A value within 100–599 can be structurally valid yet absent from the standards registry. The card shows its class and flags the assignment gap.
- Status versus port
- Three-digit status-range values are also valid ports. Standardized HTTP statuses rank higher; the port possibility remains visible as a secondary interpretation.
- Nonstandard framework codes
- Some servers and proxies publish extension codes. Their local documentation controls the meaning; tryb does not silently promote them into IANA standards.
Common mistakes
- Treating every 2xx response as evidence that the requested business operation completed correctly.
- Retrying every 5xx response without idempotency or backoff.
- Using a nonstandard code without documenting which component defines it.
- Diagnosing an application solely from the status code while ignoring method, headers, and response body.