Base64 uses + and / — which have reserved meanings in URLs. Base64URL (RFC 4648 §5) substitutes: + → -, / → _, and typically drops the = padding. That’s why JWTs use Base64URL, not classic Base64 — JWT segments appear in URLs and HTTP headers where + and / would break parsing. If you’re encoding a binary blob for a URL, query string, or JWT: Base64URL. For email attachments, PEM certs, HTTP request bodies: classic Base64. Convert between both formats with the Base64 converter.
All questions
What is the difference between Base64 and Base64URL?
Read the full guide
What Is a JWT?
JWT (JSON Web Token) is the dominant format for API authentication, OAuth access tokens, and stateless session management. Three base64-encoded segments carry the header, claims, and signature — anyone can read them, but only the key holder can produce a valid token.