Tag
Conditional Requests
Use HTTP validators and preconditions to avoid unnecessary transfers, prevent conflicting writes, and serve cached responses safely. This curated hub brings together 8 related resources.
412 Precondition Failed
The server doesn't meet one or more preconditions specified in request headers. Learn about conditional requests and how to prevent conflicts.
428 Precondition Required
The server requires the request to be conditional. Learn when to use 428 Precondition Required to prevent lost updates and race conditions.
HTTP Headers and Caching: A Practical Guide
Master HTTP caching with Cache-Control, ETag, Last-Modified, and conditional request headers. Learn how to optimize performance with proper cache strategies.
If-Match Header
Learn how the If-Match header makes requests conditional based on ETag matching. Prevent conflicts and lost updates in concurrent editing scenarios.
If-Modified-Since Header
Learn how the If-Modified-Since header requests resources only if modified since a specific date. Reduce bandwidth with efficient conditional caching.
If-None-Match Header
Learn how the If-None-Match header makes conditional requests using ETags. Avoid downloading unchanged resources and reduce bandwidth with cache validation.
If-Range Header
Learn how the If-Range header requests partial content only if the resource is unchanged. Efficiently resume downloads without re-fetching entire files.
If-Unmodified-Since Header
Learn how the If-Unmodified-Since header makes requests conditional on resources not being modified. Prevent conflicts in concurrent update scenarios.