Header and payload
JWTs are split into header, payload and signature sections. Formalint decodes the readable JSON sections so claims are easier to inspect.
Browser-based developer tools
JWT Decoder
Decode token headers and payloads, inspect common claims and check expiration times locally in the browser.
Decoding is not signature verification. Never trust a JWT only because it can be decoded.
Reference notes
JWT inspection without a backend
Expiration claims
Common numeric date claims such as exp, iat and nbf are converted into ISO timestamps to make debugging authentication flows easier.
No verification
A decoded JWT can still be forged. Production systems must verify the signature, issuer, audience and expiration using trusted server-side code.