JWT Decoder & Encoder: Inspect JSON Web Tokens Instantly

What Is a JWT Token? (JSON Web Token Explained)

A JWT (JSON Web Token) is a compact, URL-safe token format defined in RFC 7519, used to securely transmit information between parties as a digitally signed JSON object. JWTs are the standard mechanism for stateless authentication in modern web applications - the server encodes user identity and permissions into the token and signs it, so subsequent requests can be verified without a database lookup.

A JWT consists of three Base64url-encoded sections separated by dots (.):

JWTs are widely used in REST APIs, microservices, single-page applications (React, Angular, Vue), and mobile app backends. To encrypt the payload, use JWE (JSON Web Encryption) instead of the standard JWT (technically JWS - JSON Web Signature).

How to Decode a JWT Token Online (Step by Step)

1. Copy your JWT token from your application, browser developer tools (Application > Cookies or Authorization headers), or API response
2. Paste the full token string into the input field above - it must start with eyJ (Base64url-encoded opening of a JSON object)
3. The decoded header and payload appear instantly. Review all claims, the signing algorithm, and the token type
4. Check the Token Status banner to see if the token is valid, expired, or not yet active, along with a live countdown timer
5. Review the Security Audit panel for warnings like the use of the none signature algorithm or missing expiry times
6. Use the Claims Breakdown table to interpret standard claims (such as exp, sub, iss) alongside their official RFC definitions
7. Expand the Verification Code Snippets section to copy ready-to-use backend validation code in JS, Python, Go, Java, or cURL

JWT vs Session Tokens: When Should You Use Each?

Use JWT when: Building stateless REST APIs, microservice authentication, mobile backends, short-lived tokens (15 min–1 hr), or cross-domain authentication.

Use sessions when: Building traditional server-side web apps, when you need immediate revocation, long-lived user sessions, or high-security applications.

JWT Signing Algorithms Explained: HS256 vs RS256 vs ES256

RS256 is recommended for most production systems because the public key can be distributed to any service that needs to verify tokens, without exposing the signing secret.

JWT Security Best Practices for Developers (2026)

• Always verify the JWT signature on the server before trusting any claims
• Set a reasonable expiration time - short-lived tokens (15 min–1 hr) reduce the impact of token theft
• Never store sensitive data like passwords or private keys in the JWT payload (it is NOT encrypted)
• Use HTTPS for all token transmission - never send tokens over unencrypted connections
• Store tokens securely - use httpOnly cookies rather than localStorage to prevent XSS attacks
• Implement token refresh mechanisms for long-lived sessions using short-lived access tokens + refresh tokens
• Validate the iss and aud claims to prevent token substitution attacks
• Never accept tokens with alg: none - this disables signature verification and is a known attack vector
• Use a JWT blocklist or short expiry for immediate revocation when needed

How to Decode a JWT Token in Code

These examples decode the payload without signature verification - the same operation this browser tool performs.

// Decode without verification (read-only, same as this tool)
function decodeJWT(token) {
  const [header, payload] = token.split('.');
  const decode = str => JSON.parse(atob(str.replace(/-/g, '+').replace(/_/g, '/')));
  return { header: decode(header), payload: decode(payload) };
}

const { header, payload } = decodeJWT(yourToken);
console.log(payload.exp); // expiry timestamp

import base64, json

def decode_jwt_payload(token):
    payload = token.split('.')[1]
    # Add padding
    payload += '=' * (4 - len(payload) % 4)
    return json.loads(base64.urlsafe_b64decode(payload))

claims = decode_jwt_payload(your_token)
print(claims['exp'])  # expiry timestamp

import (
    "encoding/base64"
    "encoding/json"
    "strings"
)

func decodeJWTPayload(token string) (map[string]interface{}, error) {
    parts := strings.Split(token, ".")
    payload, _ := base64.RawURLEncoding.DecodeString(parts[1])
    var claims map[string]interface{}
    json.Unmarshal(payload, &claims)
    return claims, nil
}

JWT vs Session Tokens: When Should You Use JWTs?

JWTs are ideal for stateless authentication where the server does not need to store session information. Because all user data is encoded in the token itself, the server can verify identity without a database lookup. They are widely used in REST APIs, microservices, single-page applications, and mobile app backends. However, JWTs should not be used to store sensitive data in the payload since the payload is only Base64url-encoded, not encrypted.