Random HTTP Header Generator

Generate realistic HTTP header lines — request, response, or both — using standard, RFC-defined header names paired with plausible, format-correct values. Handy for mock servers, parser fuzzing, and documentation.

How it works

An HTTP header is a Name: value pair on its own line. This tool keeps separate tables of standard request and response headers, then for each chosen header it generates a value that matches that header’s expected shape:

Authorization: Bearer <random token>
Content-Type:  <random MIME type>
Date:          <current GMT date>
Cache-Control: <random directive>

Names are real and standard; values are fabricated but format-correct, so the output parses like genuine traffic without exposing any real data.

Tips and notes

Header names are case-insensitive per the spec, though the canonical capitalization (such as Content-Type) is conventional and used here. When feeding the output into a strict parser, keep the single space after the colon and one header per line — both are what well-behaved clients and servers emit.

When this tool is genuinely useful

Building a mock API server. When writing integration tests against a stub server, you need realistic response headers — not just Content-Type: application/json. Generating a set of plausible Cache-Control, ETag, X-Request-Id, and Vary headers makes the mock behave like a real server and surfaces header-parsing bugs your code might not hit with minimal stubs.

Fuzzing an HTTP parser or middleware. Parser vulnerabilities — header injection, malformed-value handling, oversized header lines — are best found by feeding a parser a wide variety of header combinations it was not written to expect. Randomised but format-valid headers let you explore the normal-value space before moving to edge cases.

Teaching and documentation. When writing a tutorial on how HTTP headers work, you need plausible examples that do not expose credentials or real IP addresses. The generator produces illustrative Authorization, Set-Cookie, and User-Agent lines that read like real traffic.

Populating test-data fixtures. If your test suite needs a JSON array of realistic HTTP exchange objects, you can generate batches of request/response pairs here and paste them straight into your fixture files.

Request vs. response headers — a quick guide

Some headers appear in both directions: Content-Type in a request body (POST/PUT) or in a response body is valid, for instance.

Pasting the output into common tools

• curl: save the block to a file and pass it with curl -H @headerfile. Each Name: value line in the file becomes a request header.
• Postman / Insomnia: paste lines into the Headers tab; the tool splits on : automatically.
• Node.js test with node-fetch or undici: convert lines to a Headers object by splitting each line on the first : .
• OpenAPI / Swagger stub: copy specific response headers into the headers map of a response object in your spec.