JWT is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed.

Absolutely not! Our tool runs entirely using client-side JavaScript within your web browser. Your token is decoded instantly on your device and no data is ever transmitted across the internet.

A JWT always consists of 3 parts separated by dots `.`: **Header** (Contains the signing algorithm and token type), **Payload** (Contains the actual claims/data such as user ID, roles, and expiration time), and **Signature** (Used to verify that the token hasn't been tampered with).

An invalid token is usually caused by: missing dot `.` separators, containing characters not part of the Base64Url standard, or the decoded data not forming a valid JSON string.