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Verify Signature

Secret / Public Key

What is JWT?

JWT (JSON Web Token, RFC 7519) is an open standard for securely transmitting information between parties as a compact JSON object. It is commonly used for authentication and authorization.

Structure

A JWT consists of three Base64URL-encoded parts separated by dots: Header.Payload.Signature. The header specifies the token type and signing algorithm. The payload contains the claims. The signature verifies integrity.

Supported Algorithms

HMAC (HS256/384/512), RSA (RS256/384/512), RSA-PSS (PS256/384/512), and ECDSA (ES256/384/512). The unsigned `alg=none` is rejected for safety.

Accepted Key Formats

HMAC: any UTF-8 string. Asymmetric: PEM only — PKCS8 (-----BEGIN PRIVATE KEY-----) for signing, SPKI (-----BEGIN PUBLIC KEY-----) for verifying. PKCS1, SEC1, encrypted PEM, and X.509 certificates are not accepted; the tool will tell you the exact openssl command to convert them.