JSON Web Token (JWT) — Structure Validation Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching json web token (jwt) — structure validation, ported and verified for Python. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. 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

# JSON Web Token (JWT) — Structure Validation
# ReDoS-safe | RegexVault — Security > API Keys & Tokens

import re

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

def validate_json_web_token_jwt_structure_validation(value: str) -> bool:
    return bool(json_web_token_jwt_structure_validation_pattern.fullmatch(value))

# Example
print(validate_json_web_token_jwt_structure_validation("eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Security > API Keys & Tokens 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

Structure only — does not validate header algorithm, payload claims, expiry, or signature. Three segments: header (base64url) + payload (base64url) + signature (base64url, may be empty for 'none' algorithm — always reject 'none'). Capture groups: 1=header, 2=payload, 3=signature.