What is JWT Base64Url Encoding?
JWT (JSON Web Tokens) use Base64Url encoding to safely transmit data between systems. Unlike standard Base64, Base64Url replaces '+' with '-' and '/' with '_' for URL-friendly formatting. This encoding creates three parts: header, payload, and signature.
Why Decode JWT Tokens?
Decoding JWT tokens helps you:
- Verify token contents (like expiration dates)
- Troubleshoot authentication issues
- Inspect claims without modifying the token
- Understand security vulnerabilities
Never decode tokens from untrusted sources without proper validation.
How to Decode Base64Url in JWT
Follow these steps to decode any JWT token:
1. Split the token into three parts using "." as separators
2. Take the middle section (payload) for decoding
3. Use an online decoder or code like this:
atob(payload.replace(/-/g, '+').replace(/_/g, '/'))
4. The decoded text will show JSON claims like:
{
"sub": "1234567890\