Base64 URL-Safe (No Padding) Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching base64 url-safe (no padding), 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

# Base64 URL-Safe (No Padding)
# ReDoS-safe | RegexVault — Web & Network > Misc

import re

base64_urlsafe_no_padding_pattern = re.compile(r'^[A-Za-z0-9\-_]+$')

def validate_base64_urlsafe_no_padding(value: str) -> bool:
    return bool(base64_urlsafe_no_padding_pattern.fullmatch(value))

# Example
print(validate_base64_urlsafe_no_padding("SGVsbG8"))  # 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

Used in JWTs, OAuth tokens, and URL-embedded data. Empty string is excluded here since a zero-length token is semantically invalid in most use cases.