Domain Name (Basic Hostname) Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching domain name (basic hostname), 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

# Domain Name (Basic Hostname)
# ReDoS-safe | RegexVault — Web & Network > Domain

import re

domain_name_basic_hostname_pattern = re.compile(r'^(?:[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.)*[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?$')

def validate_domain_name_basic_hostname(value: str) -> bool:
    return bool(domain_name_basic_hostname_pattern.fullmatch(value))

# Example
print(validate_domain_name_basic_hostname("example.com"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Domain 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

Does not validate TLD existence or length. Each label limited to 63 chars per RFC 1034. Total hostname should be ≤253 chars (not enforced here).