JWT Decoder Online — Decode JSON Web Tokens Instantly

Paste any JSON Web Token (JWT) to instantly decode and inspect its three parts: the header, payload (claims), and signature. Our free online JWT decoder runs entirely in your browser — your token never leaves your machine. Ideal for debugging authentication flows, inspecting OAuth 2.0 access tokens, validating OpenID Connect ID tokens, and auditing JWT claims like iss, sub, exp, and aud.

• Privacy-First: 100% client-side — no token is ever sent to a server.
• Instant Decode: Paste a JWT and see the decoded header and payload in milliseconds.
• Expiry Detection: exp, iat, and nbf timestamps shown in human-readable local time.
• Works with all algorithms: HS256, RS256, ES256, PS256, and any other algorithm — the decoder only reads the header and payload, which are always Base64URL encoded.

What is a JWT? Structure of a JSON Web Token

A JSON Web Token is a compact, URL-safe means of representing claims between two parties, defined in RFC 7519. A JWT consists of exactly three Base64URL-encoded segments separated by dots:

• Header — specifies the token type (typ: "JWT") and signing algorithm (alg: "HS256", "RS256", etc.).
• Payload (Claims) — contains arbitrary JSON claims. Standard registered claims include iss (issuer), sub (subject), aud (audience), exp (expiration time), iat (issued at), and nbf (not before).
• Signature — a cryptographic signature computed over the header + payload using the secret or private key. Verifying the signature requires the key — the decoder shows the raw signature bytes for inspection.

Because the header and payload are only Base64URL-encoded (not encrypted), sensitive data must never be stored in a JWT payload unless the token is additionally wrapped in a JWE (JSON Web Encryption). Use JWTs to carry non-sensitive identity claims, not passwords or PII.

Common JWT Use Cases: OAuth 2.0, OpenID Connect & API Authentication

JWTs are the backbone of modern web authentication. Understanding how to decode JWT tokens online is an essential skill for any backend or full-stack developer:

• OAuth 2.0 Access Tokens: Providers like Auth0, Okta, AWS Cognito, and Google issue JWTs as access tokens. Decoding them reveals scopes, user ID, and token lifetime.
• OpenID Connect ID Tokens: ID tokens carry the authenticated user's identity claims (email, name, picture) signed by the authorization server.
• API Gateway Authorization: AWS API Gateway, Kong, and Nginx all support JWT validation middleware. Paste a token here to verify claims without hitting the server.
• Microservices & Service Mesh: Internal services pass JWTs for service-to-service authentication (e.g., in Kubernetes with Istio or Envoy). Decode tokens to debug 401/403 errors.
• Firebase & Supabase Auth: Both platforms use JWTs for session management. Inspect firebase:sign_in_provider or Supabase role claims directly.

Decode JWT in JavaScript, Python & Go

While our online JWT decoder is perfect for quick inspection, here are the standard libraries for programmatic JWT decoding in popular languages:

// npm install jsonwebtoken
const jwt = require('jsonwebtoken');

// Decode without verification
const decoded = jwt.decode(token);

// Decode & verify signature
const verified = jwt.verify(
  token,
  process.env.JWT_SECRET
);

# pip install PyJWT
import jwt

# Decode without verification
claims = jwt.decode(
  token,
  options={"verify_signature": False}
)

# Decode & verify
claims = jwt.decode(
  token,
  secret,
  algorithms=["HS256"]
)

// go get github.com/golang-jwt/jwt/v4
import "github.com/golang-jwt/jwt/v4"

token, err := jwt.Parse(
  tokenStr,
  func(t *jwt.Token) (any, error) {
    return []byte(secret), nil
  },
)
claims := token.Claims
  (jwt.MapClaims)

JWT Security Best Practices: What to Check When Decoding

When you parse a JWT token, always verify these security-critical claims:

• exp (Expiration): Never accept expired tokens. Our decoder highlights expired tokens automatically.
• aud (Audience): Confirm the token was issued for your service. Accepting tokens issued for other audiences is a critical security vulnerability (OWASP Top 10).
• iss (Issuer): Validate the token was signed by a trusted authority, not a malicious third party.
• alg (Algorithm): Never accept alg: "none" — this disables signature verification and is a known attack vector.
• Scope / Roles claims: Inspect custom claims like roles, scope, or permissions for proper authorization enforcement.