1. Introduction

To aid debugging (both by humans and automated tools), HTTP caches often append header fields to a response explaining how they handled the request. Unfortunately, the semantics of these header fields are often unclear, and both the semantics and syntax used vary between implementations.

This specification defines a new HTTP response header field, "Cache-Status", for this purpose with standardized syntax and semantics.

1.1. Notational Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

This document uses the following terminology from Section 3 of [STRUCTURED-FIELDS] to specify syntax and parsing: List, String, Token, Integer, and Boolean.

This document also uses terminology from [HTTP] and [HTTP-CACHING].