HTTP Header Field Name Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching http header field name, ported and verified for Python. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# HTTP Header Field Name
# ReDoS-safe | RegexVault — Web & Network > HTTP

import re

http_header_field_name_pattern = re.compile(r'^[a-zA-Z][a-zA-Z0-9\-!#$%&'*+.^_`|~]{0,99}$')

def validate_http_header_field_name(value: str) -> bool:
    return bool(http_header_field_name_pattern.fullmatch(value))

# Example
print(validate_http_header_field_name("Content-Type"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > HTTP category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

HTTP header names are case-insensitive per RFC 7230 but conventionally Title-Case. Reject headers with spaces — they indicate header injection attempts.