webheaders

Webheaders, commonly referred to as HTTP headers, are metadata sent along with HTTP requests and responses. They convey information about the client, the resource being requested, and how the message should be processed. Headers are key-value pairs that accompany the start line of a message and are separated from the body by a blank line.

Each header line consists of a field-name followed by a colon and a field-value. Field names are case-insensitive. In both requests and responses, headers can control caching, encoding, authentication, content type, and multiple other aspects of handling the message.

Common request headers include Host, User-Agent, Accept, Accept-Language, Accept-Encoding, and Cookie. Common response headers include Content-Type, Content-Length, Cache-Control, ETag, Last-Modified, Set-Cookie, and Location. General headers such as Date, Connection, and Server accompany both directions.

HTTP/2 and newer versions use a binary framing layer, but the headers remain name-value pairs, often transmitted with compression via HPACK to reduce overhead.

Headers enable content negotiation, caching directives, compression, authentication, and redirection. They also support security and privacy policies through headers such as Content-Security-Policy, X-Frame-Options, X-Content-Type-Options, and Cross-Origin Resource Sharing (CORS) headers.

Privacy and security considerations include avoiding leakage of sensitive data in headers, minimizing unnecessary User-Agent details, and employing TLS. Referrer headers can reveal navigation paths, so a Referrer-Policy may be used to limit exposure.

In practice, headers influence how servers, intermediaries, and clients behave, affecting caching, load balancing, and the handling of cookies across requests.