If-Unmodified-Since
IANA permanent
request
RFC 9110
2 spellings
Declared by 10 providers across 203 published specification files in the APIs.io network.
A count here is providers whose published contract declares this header — not
providers who send it. Response headers set at the edge rarely appear in an OpenAPI at all, so a low
number can measure documentation practice rather than deployment.
Spelled 2 ways
HTTP field names are case-insensitive (RFC 9110 §5.1), so every spelling below is the same header on the wire. A contract is not the wire: generated clients key off the string, and a developer reading two of these sees two different headers.
If-Unmodified-Sinceif-unmodified-since
The registry
| Status | permanent |
|---|---|
| Reference | RFC 9110, Section 13.1.4: HTTP Semantics |
Providers declaring it (10)
amazon-s3 armor aws-s3 cloudflare-r2 engineering-platform etsi microsoft-azure nhost oracle val-town
Explore
All headers Conditional Requests & Concurrency Guidance on headers.apievangelist.com