URL-Encoded Form Data Body Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching url-encoded form data body, 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

# URL-Encoded Form Data Body
# ReDoS-safe | RegexVault — Web & Network > Misc

import re

urlencoded_form_data_body_pattern = re.compile(r'^[a-zA-Z0-9%+\-_.~!$'()*,;:@/?]+(?:=[a-zA-Z0-9%+\-_.~!$'()*,;:@/?]*)?(?:&[a-zA-Z0-9%+\-_.~!$'()*,;:@/?]+(?:=[a-zA-Z0-9%+\-_.~!$'()*,;:@/?]*)?)*$')

def validate_urlencoded_form_data_body(value: str) -> bool:
    return bool(urlencoded_form_data_body_pattern.fullmatch(value))

# Example
print(validate_urlencoded_form_data_body("key=value"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Misc 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

Spaces are encoded as + (form encoding) or %20 (percent encoding). Both are valid. The pattern accepts key-only parameters (no = sign) and empty values (key=).