JWT Decoder

Decode and inspect JSON Web Tokens (JWT) with claim explanations

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🔑What is a JWT (JSON Web Token)?

JSON Web Token (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.

JWTs consist of three parts separated by dots: Header (algorithm and token type),Payload (claims/data), and Signature (verification). Each part is Base64URL encoded.

Common JWT Claims

iss

Issuer - Who created and signed this token

sub

Subject - Who this token is about

aud

Audience - Who this token is intended for

exp

Expiration Time - When this token expires

nbf

Not Before - Token is not valid before this time

iat

Issued At - When this token was issued

jti

JWT ID - Unique identifier for this token

JWT Security Best Practices

✅Always validate the signature on the server side before trusting any claims

✅Use short expiration times (15-60 minutes) for access tokens

✅Never store sensitive data (passwords, PII) in the payload

✅Use HTTPS exclusively to prevent token interception

✅Implement token refresh mechanisms with secure refresh tokens

✅Use asymmetric algorithms (RS256, ES256) for distributed systems

JWT vs Traditional Sessions

JWTs offer a stateless authentication mechanism, meaning the server doesn't need to store session data. This makes JWTs ideal for microservices architectures and horizontally scaled applications where maintaining session state across servers is challenging.

However, JWTs have trade-offs. They cannot be invalidated before expiration without additional infrastructure (like a token blacklist). Traditional sessions stored server-side can be immediately revoked but require shared storage in distributed systems.

For most web applications, a hybrid approach works best: short-lived JWTs for API authentication combined with secure, HTTP-only refresh tokens stored in cookies for session management.

JWT Signing Algorithms

HS256 (HMAC-SHA256)

Symmetric algorithm using a shared secret. Fast and simple, but the same key is used for signing and verification. Best for single-server applications.

RS256 (RSA-SHA256)

Asymmetric algorithm using public/private key pairs. Private key signs, public key verifies. Ideal for distributed systems and third-party integrations.