base64url in JWTs
A JWT has three dot-separated parts: header, payload, signature. Header and payload are JSON objects encoded with base64url — standard base64 with + → -, / → _, and padding often omitted.
base64app converts URL-safe input when auto-repair is enabled, so you can paste JWT segments for inspection.
Not encryption
Base64 in JWTs is encoding, not encryption. Anyone can decode the header and payload to read claims — signatures verify integrity, not secrecy.