About Base64, URL encoding and JWTs

Base64 represents binary data as ASCII text and is used everywhere from email attachments to data URIs. This tool is UTF-8 safe, so emoji and non-Latin characters round-trip correctly. URL encoding (percent-encoding) escapes characters that are not allowed in URLs — paste either side and the other updates live.

A JSON Web Token (JWT) consists of three Base64URL parts: header, payload and signature. The decoder shows the header and payload as formatted JSON and converts the iat/nbf/exp claims to local time with an expiry check. Everything runs client-side — your token is never sent to any server, and the signature is not (and cannot be) verified without the secret key. Related tool: JSON Formatter & Validator.