JWT Encoder/Decoder

JWT Encoder/Decoder - Create and Decode JSON Web Tokens Online

A powerful online JWT (JSON Web Token) encoder and decoder tool that allows you to create new JWT tokens or decode, inspect, and understand existing tokens instantly. Encode header and payload with HMAC signing (HS256, HS384, HS512), or decode the header (JOSE header), payload (claims), and signature of any JWT token. View standard claims like issuer, subject, audience, expiration time, and more. Perfect for developers, security professionals, and anyone working with JWT-based authentication, OAuth 2.0, OpenID Connect, and API security.

What is JWT (JSON Web Token)?

JWT (JSON Web Token) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. It's a compact, URL-safe token format that's digitally signed to verify authenticity and integrity.

JWT Structure:
A JWT consists of three parts separated by dots (.): header.payload.signature

1. Header (JOSE Header):
- Contains token metadata
- Specifies the signing algorithm (e.g., HS256, RS256, ES256)
- Defines the token type (usually "JWT")
- Example: {"alg":"HS256","typ":"JWT"}

2. Payload (Claims):
- Contains the actual data (claims)
- Includes registered claims (iss, exp, sub, aud, etc.)
- Can include custom claims (user ID, roles, permissions, etc.)
- Example: {"sub":"1234567890","name":"John Doe","iat":1516239022}

3. Signature:
- Verifies the token hasn't been tampered with
- Created by encoding the header and payload, then signing with a secret key
- Different algorithms use different signing methods

Common Uses:
- Authentication: User login sessions
- Authorization: Access control and permissions
- Information Exchange: Secure data transmission
- API Security: Stateless authentication for REST APIs
- Single Sign-On (SSO): Cross-domain authentication
- OAuth 2.0 & OpenID Connect: Token-based authorization

JWT is base64url encoded (not encrypted), which means anyone can decode and read the contents. The signature ensures the token hasn't been modified, but doesn't encrypt the data. Never put sensitive information like passwords or credit card numbers in a JWT payload.

How do I decode a JWT token?

Decoding a JWT token is simple with this tool:

1. Copy your JWT token (the long string starting with eyJ...)
2. Paste it into the "JWT Token" input field
3. Click the "Decode JWT" button
4. View the decoded results:
- Header: Shows algorithm and token type
- Payload: Shows all claims (data)
- Signature: Shows the signature part (base64url encoded)
- Standard Claims: Human-readable interpretation of common claims
- Token Info: Algorithm, type, and expiration status

Example JWT:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

Decoded Header:
{
"alg": "HS256",
"typ": "JWT"
}

Decoded Payload:
{
"sub": "1234567890",
"name": "John Doe",
"iat": 1516239022
}

The tool automatically:
- Validates the JWT format (3 parts separated by dots)
- Base64url decodes the header and payload
- Parses the JSON structure
- Formats the output for readability
- Identifies and explains standard claims
- Checks token expiration status
- Shows human-readable timestamps for date claims

What are JWT claims?

JWT claims are the statements or pieces of information contained in the payload section of a JWT token. Claims are name-value pairs that represent data about the user or the token itself.

Types of Claims:

1. Registered Claims (Standard/Reserved):
These are predefined claims recommended by the JWT specification:

- iss (Issuer): Who created and signed the token
Example: "iss": "https://auth.example.com"

- sub (Subject): The principal subject of the token (usually user ID)
Example: "sub": "1234567890" or "sub": "[email protected]"

- aud (Audience): Who the token is intended for (recipient)
Example: "aud": "https://api.example.com"

- exp (Expiration Time): When the token expires (Unix timestamp)
Example: "exp": 1735689600 (must reject token after this time)

- nbf (Not Before): Token is not valid before this time (Unix timestamp)
Example: "nbf": 1735603200

- iat (Issued At): When the token was created (Unix timestamp)
Example: "iat": 1735603200

- jti (JWT ID): Unique identifier for the token
Example: "jti": "abc123xyz" (prevents replay attacks)

2. Public Claims:
Custom claims that should be registered in the IANA JWT Registry or use collision-resistant names:
Example: "email": "[email protected]", "email_verified": true

3. Private Claims:
Custom claims agreed upon between parties:
Example: "role": "admin", "permissions": ["read", "write"], "department": "IT"

Best Practices:
- Keep payload small (JWT is included in every request)
- Don't include sensitive data (JWT is readable by anyone)
- Always include 'exp' claim to limit token lifetime
- Use 'iat' to track when token was issued
- Use 'jti' for token revocation mechanisms
- Validate all claims on the server side

Example Payload with Multiple Claims:
{
"iss": "https://auth.example.com",
"sub": "user123",
"aud": "https://api.example.com",
"exp": 1735689600,
"iat": 1735603200,
"name": "John Doe",
"email": "[email protected]",
"role": "admin",
"permissions": ["read", "write", "delete"]
}

How do I verify a JWT signature?

JWT signature verification is a critical security step that ensures the token hasn't been tampered with. However, signature verification MUST be done on the server-side, not in the browser.

Why Server-Side Only?
- Requires the secret key (symmetric algorithms) or private key (asymmetric algorithms)
- Exposing keys in client-side code would compromise security
- Anyone could modify tokens if keys were public
- Verification in browser JavaScript is NOT secure

Signature Verification Process:

1. For Symmetric Algorithms (HS256, HS384, HS512):
- Server has the secret key
- Takes header + payload from the JWT
- Signs them with the secret key using the specified algorithm
- Compares the resulting signature with the JWT's signature
- If they match, token is valid and unmodified

2. For Asymmetric Algorithms (RS256, RS384, RS512, ES256, ES384, ES512):
- Token is signed with a private key
- Server verifies with the corresponding public key
- Public key can be shared safely
- Only holder of private key can create valid signatures

Server-Side Verification (Example concepts):

Node.js (jsonwebtoken library):
const jwt = require('jsonwebtoken');
try {
const decoded = jwt.verify(token, secretKey);
// Token is valid
} catch (error) {
// Token is invalid or expired
}

Python (PyJWT library):
import jwt
try:
decoded = jwt.decode(token, secret_key, algorithms=["HS256"])
# Token is valid
except jwt.InvalidTokenError:
# Token is invalid or expired

What This Tool Does:
- Decodes the JWT structure (header, payload, signature)
- Displays the claims and metadata
- Shows which algorithm was used
- Checks expiration status
- Does NOT verify the signature (no secret key)

Important Security Notes:
- NEVER share your secret keys or private keys
- NEVER verify signatures in client-side JavaScript
- Always verify signatures on your backend server
- Use HTTPS to transmit JWT tokens
- Store JWTs securely (httpOnly cookies or secure storage)
- Implement token expiration and refresh mechanisms
- Use strong secret keys (at least 256 bits for HS256)

This decoder tool is for:
✓ Inspecting JWT structure
✓ Debugging authentication issues
✓ Understanding claims and metadata
✓ Checking token expiration
✓ Educational purposes

NOT for:
✗ Production signature verification
✗ Security validation
✗ Trust decisions

What are the different JWT algorithms?

JWT supports multiple cryptographic algorithms for signing tokens, divided into two main categories:

1. HMAC (Symmetric Algorithms):
Use the same secret key for both signing and verification.

- HS256 (HMAC SHA-256):
* Most commonly used
* Fast and efficient
* 256-bit secret key recommended
* Good for server-to-server authentication
* Both parties must securely share the secret key

- HS384 (HMAC SHA-384):
* Stronger than HS256
* 384-bit hash
* Slightly larger signature

- HS512 (HMAC SHA-512):
* Strongest HMAC option
* 512-bit hash
* Largest signature size

When to use HMAC:
- Internal APIs and microservices
- Server-to-server communication
- When both parties can securely share a secret
- When performance is critical
- Simpler key management

2. RSA (Asymmetric Algorithms):
Use public-private key pairs. Sign with private key, verify with public key.

- RS256 (RSA SHA-256):
* Very popular for public APIs
* Public key can be shared safely
* Larger signature size than HMAC
* Slower than HMAC

- RS384 (RSA SHA-384):
* Stronger than RS256
* Larger keys and signatures

- RS512 (RSA SHA-512):
* Strongest RSA option
* Largest overhead

When to use RSA:
- Public APIs (OAuth 2.0, OpenID Connect)
- Multiple consumers need to verify tokens
- When public key distribution is needed
- Third-party integrations
- Higher security requirements

3. ECDSA (Elliptic Curve - Asymmetric):
Use elliptic curve cryptography. Smaller keys than RSA with similar security.

- ES256 (ECDSA P-256 SHA-256):
* Modern and efficient
* Smaller signatures than RSA
* Same security as RSA with smaller keys
* Growing in popularity

- ES384 (ECDSA P-384 SHA-384):
* Stronger than ES256
* Good balance of security and performance

- ES512 (ECDSA P-521 SHA-512):
* Highest ECDSA security
* Note: P-521 curve (not P-512)

When to use ECDSA:
- Mobile applications (smaller signatures)
- IoT devices (efficient cryptography)
- Modern systems with ECDSA support
- When bandwidth is limited

4. PS256, PS384, PS512 (RSA-PSS):
RSA with Probabilistic Signature Scheme (more secure padding).

5. EdDSA (Ed25519):
Modern elliptic curve algorithm, very fast and secure.

Algorithm Comparison:

Security (Strongest to Weakest):
ES512 > RS512 > PS512 > ES384 > RS384 > ES256 > RS256 > PS256 > HS512 > HS384 > HS256

Performance (Fastest to Slowest):
HS256 > HS384 > HS512 > ES256 > ES384 > ES512 > RS256 > RS384 > RS512

Signature Size (Smallest to Largest):
ES256 < HS256 < ES384 < HS384 < ES512 < HS512 < RS256 < RS384 < RS512

None Algorithm Warning:
- "alg": "none" means no signature
- NEVER accept unsigned tokens in production
- Major security vulnerability
- Always validate the algorithm

Recommendations:
- Default choice: RS256 or ES256 for public APIs
- Internal services: HS256 for simplicity and speed
- Mobile/IoT: ES256 for efficiency
- Maximum security: ES512 or RS512
- Modern systems: Consider EdDSA if supported

Always validate the algorithm on the server side to prevent algorithm substitution attacks!

Is JWT secure? What are the security considerations?

JWT can be secure when used correctly, but there are important security considerations and potential vulnerabilities to be aware of:

Security Strengths:
✓ Tamper-proof: Signature prevents modification
✓ Stateless: No server-side session storage needed
✓ Portable: Works across domains and services
✓ Standard: Well-defined specification (RFC 7519)
✓ Flexible: Supports multiple algorithms

Security Considerations & Best Practices:

1. JWT is NOT Encrypted (by default):
- Anyone can decode and read the payload
- Never store sensitive data in JWT (passwords, credit cards, SSN)
- Consider JWE (JSON Web Encryption) for encrypted tokens
- Use HTTPS to transmit JWT tokens

2. Secret Key Security:
- Use strong, random secret keys (256+ bits for HS256)
- Never commit keys to version control
- Rotate keys periodically
- Use environment variables or key management systems
- Different keys for different environments

3. Algorithm Confusion Attacks:
- Always validate the algorithm on the server
- Reject tokens with "alg": "none"
- Don't let the token dictate which algorithm to use
- Explicitly specify allowed algorithms

4. Token Expiration:
- Always include 'exp' claim
- Use short expiration times (15-60 minutes)
- Implement refresh tokens for long-lived sessions
- Check expiration on every request

5. Token Storage:
- Browser: httpOnly + Secure cookies (best for web)
- Mobile: Secure storage (Keychain, KeyStore)
- Never store in localStorage (vulnerable to XSS)
- Never store in regular cookies without httpOnly flag

6. Token Revocation:
- JWT is stateless (can't revoke by default)
- Implement token blacklist for revoked tokens
- Use short expiration + refresh tokens
- Consider JTI (JWT ID) claim for tracking
- Maintain list of revoked JTIs in Redis/database

7. Cross-Site Attacks:
- XSS (Cross-Site Scripting): Can steal tokens from localStorage
- CSRF (Cross-Site Request Forgery): Use SameSite cookie attribute
- Use Content Security Policy (CSP) headers
- Sanitize user input

8. Replay Attacks:
- Use JTI (JWT ID) claim with one-time use
- Track used tokens
- Implement 'nbf' (not before) claim
- Use nonce for critical operations

9. Key Management:
- Use separate keys for different purposes
- Implement key rotation strategy
- Use public-private key pairs (RS256) when appropriate
- Consider AWS KMS, Azure Key Vault, or HashiCorp Vault

10. Validation:
- Always verify signature server-side
- Validate all claims (iss, aud, exp, nbf)
- Check token hasn't been revoked
- Validate token structure and format
- Use established libraries (don't implement JWT manually)

11. Information Disclosure:
- JWT payload is readable (not encrypted)
- Don't include: passwords, credit cards, SSN, secrets
- Minimize payload size
- Only include necessary claims
- Consider PII (Personally Identifiable Information) regulations

12. Transmission Security:
- Always use HTTPS/TLS
- Never send JWT over unencrypted HTTP
- Consider token binding to prevent token theft
- Use secure WebSocket (wss://) for real-time apps

Common Vulnerabilities:

1. None Algorithm Attack:
- Attacker changes "alg" to "none" and removes signature
- Solution: Explicitly validate algorithm

2. Algorithm Substitution:
- Change RS256 to HS256, use public key as secret
- Solution: Whitelist allowed algorithms per key

3. Weak Secret Keys:
- Short or predictable keys can be brute-forced
- Solution: Use strong random keys (256+ bits)

4. Token Leakage:
- Tokens logged in error logs or analytics
- Solution: Sanitize logs, avoid logging tokens

5. No Expiration:
- Tokens without 'exp' claim live forever
- Solution: Always set expiration

Security Checklist:
☐ Use HTTPS for all token transmission
☐ Store tokens in httpOnly cookies (web) or secure storage (mobile)
☐ Include 'exp' claim with short expiration
☐ Validate signature on every request
☐ Validate all claims (iss, aud, exp, nbf)
☐ Use strong secret keys (256+ bits)
☐ Explicitly specify allowed algorithms
☐ Never store sensitive data in JWT payload
☐ Implement refresh token mechanism
☐ Have a token revocation strategy
☐ Rotate keys periodically
☐ Use established JWT libraries
☐ Monitor for suspicious token usage
☐ Implement rate limiting
☐ Log authentication events

JWT is secure when:
✓ Used correctly with best practices
✓ Transmitted over HTTPS
✓ Stored securely
✓ Validated properly server-side
✓ Combined with other security measures

JWT is NOT secure when:
✗ Contains sensitive data
✗ Uses weak keys
✗ Stored in localStorage (web)
✗ Transmitted over HTTP
✗ Signature not validated
✗ No expiration set
✗ Algorithm not validated

What's the difference between JWT and session-based authentication?

JWT (Token-Based) and Session-Based authentication are two different approaches to managing user authentication. Each has advantages and trade-offs:

Session-Based Authentication:

How it works:
1. User logs in with credentials
2. Server creates a session and stores it in memory/database
3. Server sends session ID to client (usually in cookie)
4. Client sends session ID with each request
5. Server looks up session to verify authentication

Session Storage:
- Server: Session data stored on server (memory, Redis, database)
- Client: Only session ID stored (small string)

JWT (Token-Based) Authentication:

How it works:
1. User logs in with credentials
2. Server creates a JWT token with user information
3. Server sends JWT to client
4. Client sends JWT with each request (Authorization header)
5. Server validates JWT signature and expiration

Token Storage:
- Server: No storage needed (stateless)
- Client: Full JWT token stored (larger string)

Comparison:

1. Statefulness:
Sessions: Stateful (server stores session data)
JWT: Stateless (all data in token)

Advantage: JWT doesn't require server-side storage
Advantage: Sessions can be instantly invalidated

2. Scalability:
Sessions: Harder to scale (session sharing across servers)
- Requires sticky sessions or shared session store (Redis)
- Database queries for each request
JWT: Easier to scale (no server state needed)
- No session sharing needed
- No database queries
- Works well with microservices

3. Security:
Sessions:
✓ Can be immediately revoked
✓ Session data not visible to client
✓ Smaller attack surface (just session ID)
✗ Vulnerable to CSRF (needs CSRF tokens)
✗ Session fixation attacks

JWT:
✓ Can't be modified (signed)
✓ Works across domains
✗ Can't be easily revoked (stateless)
✗ Payload is visible (not encrypted)
✗ Larger attack surface if stored insecurely
✗ Requires careful key management

4. Performance:
Sessions:
- Database/cache lookup on each request
- Slower with large number of users
- Memory intensive on server

JWT:
- No database lookup (validate signature only)
- Faster with large number of users
- Larger payload sent with each request

5. Mobile & SPA:
Sessions:
- Complex for mobile apps
- Cookie management can be problematic
- CORS issues with cross-domain

JWT:
- Perfect for mobile apps
- Simple API authentication
- Easy cross-domain authentication
- Native mobile app friendly

6. Data Storage:
Sessions:
- Any amount of data (server-side)
- Can store complex objects
- Data never exposed to client

JWT:
- Limited data (token size grows)
- Only JSON-serializable data
- Data visible to client
- Keep payload minimal

7. Expiration & Revocation:
Sessions:
✓ Can invalidate immediately
✓ Easy to implement logout
✓ Can update session data anytime
- Session timeout easy to implement

JWT:
✗ Can't revoke (without extra infrastructure)
✗ Token valid until expiration
✓ Automatic expiration with 'exp' claim
- Need refresh token mechanism
- Blacklist required for revocation

8. Cross-Domain / Microservices:
Sessions:
- Difficult across domains
- Shared session store needed
- Cookie scope limitations

JWT:
- Perfect for cross-domain
- Works great with microservices
- Single token across multiple services
- API gateway friendly

9. Implementation Complexity:
Sessions:
- Simple to implement
- Well-established patterns
- Built into most frameworks
- Easy to understand

JWT:
- More complex to implement correctly
- Need to handle refresh tokens
- Key management required
- More security considerations

10. Use Cases:

Sessions are better for:
- Traditional web applications
- Server-side rendered apps
- When immediate revocation is critical
- Simple monolithic applications
- When you need to store lots of user data
- Banking or high-security applications

JWT is better for:
- RESTful APIs
- Mobile applications
- Single Page Applications (SPAs)
- Microservices architectures
- Cross-domain authentication
- Stateless, scalable systems
- OAuth 2.0 / OpenID Connect
- Third-party integrations

Hybrid Approach:
Many applications use both:
- Short-lived JWT access tokens (15-30 minutes)
- Long-lived refresh tokens (stored server-side)
- Refresh tokens used to get new access tokens
- Combines JWT scalability with revocation capability

Example Flow:
1. User logs in → receives JWT access token + refresh token
2. Access token used for API requests (stateless)
3. Access token expires → use refresh token to get new access token
4. Refresh token validated against database (can be revoked)
5. Logout → invalidate refresh token server-side

Recommendation:
- Simple web app: Use sessions
- API/Mobile/SPA: Use JWT
- Complex system: Use hybrid (JWT + refresh tokens)
- Microservices: Use JWT
- Need instant revocation: Sessions or hybrid
- Maximum scalability: JWT

The best choice depends on your specific requirements, architecture, and security needs!

Can I use this JWT decoder for production applications?

This JWT decoder tool is designed for development, debugging, and educational purposes, but there are important considerations for production use:

What This Tool IS Good For:

✓ Development & Debugging:
- Inspect JWT tokens during development
- Debug authentication issues
- Understand token structure
- Test token generation
- Verify claims and payload

✓ Learning & Education:
- Understand how JWT works
- Learn about JWT structure
- Study different algorithms
- Explore JWT claims
- Security education

✓ Quick Inspection:
- Check token expiration
- View token contents
- Validate token format
- Inspect claims

✓ Security Analysis:
- Analyze suspicious tokens
- Investigate security incidents
- Audit token structure
- Check for information leakage

What This Tool is NOT For:

✗ Production Verification:
- Does NOT verify signatures (no secret key)
- Cannot validate token authenticity
- Should not be used for security decisions
- Not a substitute for server-side validation

✗ Sensitive Data:
- Don't decode production tokens with sensitive data
- Remember: All decoding happens client-side
- Data is visible in browser memory
- Use with caution for tokens containing PII

Production Requirements:

For production JWT validation, you MUST:

1. Server-Side Validation:
- Always verify signatures on the server
- Use established JWT libraries
- Never trust client-side validation
- Validate all claims (exp, iss, aud, nbf)

2. Secret Key Security:
- Never expose secret keys
- Use environment variables
- Implement key rotation
- Use key management systems (AWS KMS, Azure Key Vault)

3. Security Best Practices:
- Validate algorithm
- Check token expiration
- Verify issuer and audience
- Implement token revocation
- Use HTTPS for all token transmission

4. Error Handling:
- Handle invalid tokens gracefully
- Log security events
- Implement rate limiting
- Monitor for suspicious activity

Production JWT Libraries:

Instead of using online decoders in production, use these established libraries:

Node.js:
- jsonwebtoken: Most popular, full-featured
- jose: Modern, standard-compliant
- fast-jwt: High performance

Python:
- PyJWT: Standard library
- python-jose: Comprehensive
- authlib: Full OAuth/JWT support

Java:
- jjwt (Java JWT): Popular choice
- java-jwt (Auth0): Well-maintained
- nimbus-jose-jwt: Comprehensive

PHP:
- firebase/php-jwt: Most popular
- lcobucci/jwt: Modern, flexible
- web-token: Symfony-based

Go:
- golang-jwt/jwt: Most popular
- lestrrat-go/jwx: Comprehensive

Ruby:
- ruby-jwt: Standard library

C#/.NET:
- System.IdentityModel.Tokens.Jwt: Official Microsoft
- jose-jwt: Alternative option

Security Considerations for Production:

1. Trust Boundary:
- Client-side decoding: UNTRUSTED
- Server-side validation: TRUSTED
- Always verify on server
- Never make security decisions based on client decoding

2. Data Privacy:
- JWT payload is NOT encrypted
- Anyone can read decoded data
- Be cautious with PII (Personal Identifiable Information)
- Consider using JWE for sensitive data

3. Tool Security:
- This tool is 100% client-side
- No data sent to servers
- Decoding happens in your browser
- However, be cautious with sensitive tokens
- Clear browser cache after use

When to Use This Tool:

✓ Local development environment
✓ Debugging authentication issues
✓ Learning and understanding JWT
✓ Inspecting test tokens
✓ Non-sensitive tokens
✓ Education and training

When NOT to Use This Tool:

✗ Production token validation
✗ Security-critical decisions
✗ Tokens with highly sensitive data
✗ Instead of proper server-side validation
✗ As the only validation mechanism

Proper Production Flow:

1. Client sends JWT to server
↓
2. Server validates signature using secret key
↓
3. Server checks expiration and claims
↓
4. Server makes authorization decision
↓
5. Server responds to client

Never:
1. Client decodes JWT
↓
2. Client checks expiration
↓
3. Client makes security decision ✗ WRONG!

Recommendation:

Use this tool for:
- Development and debugging
- Understanding JWT structure
- Inspecting test tokens
- Education purposes

For production:
- Implement server-side validation
- Use established JWT libraries
- Follow security best practices
- Never trust client-side validation
- Implement proper error handling
- Use logging and monitoring

Remember: This is a tool to help you understand and debug JWT tokens, not to replace proper security implementation. Always validate JWT tokens on your backend server in production applications!

Is my JWT token safe when using this decoder?

Yes, your JWT token is completely safe and private when using this decoder. Here's why:

Privacy & Security Features:

✓ 100% Client-Side Processing:
- All decoding happens in your browser
- JavaScript runs locally on your computer
- No server-side processing
- No network requests made

✓ No Data Transmission:
- Your JWT never leaves your computer
- No data sent to any server
- No API calls
- No external services

✓ No Storage:
- We don't store any tokens
- No logging of data
- No cookies tracking your tokens
- No analytics on token data

✓ No Tracking:
- We don't track what tokens you decode
- No analytics on decoded data
- Privacy-focused design

✓ Works Offline:
- After loading the page, works without internet
- Disconnect and it still works
- Proves no data transmission

✓ Open Source:
- Code is visible in page source
- You can verify the implementation
- Transparent operation

How to Verify Privacy:

1. Check Network Tab:
- Open browser DevTools (F12)
- Go to Network tab
- Decode a JWT token
- Observe: No network requests made

2. Offline Test:
- Load this page
- Disconnect from internet
- Try decoding a token
- It still works!

3. Review Source Code:
- View page source
- Check the JavaScript code
- Verify no external calls

However, Important Reminders:

⚠️ JWT is NOT Encrypted:
- JWT payload is Base64-encoded (not encrypted)
- Anyone with the token can decode it
- Don't put sensitive data in JWT payloads
- This applies to ALL JWT decoders (not just this one)

⚠️ Browser Security:
- Decoding happens in browser memory
- Be cautious on shared computers
- Clear browser cache after use on public computers
- Use private/incognito mode for sensitive tokens

⚠️ Screenshot/Screen Sharing:
- Be careful when screenshotting
- Watch out during screen sharing
- Decoded tokens are visible on screen

⚠️ Browser Extensions:
- Some extensions can read page content
- Be aware of installed extensions
- Use trusted browser profiles

⚠️ Public Computers:
- Avoid using on public/shared computers
- Clear browser data after use
- Use private browsing mode

Best Practices:

1. Development Tokens:
✓ Safe to decode development tokens
✓ Safe to decode test tokens
✓ Safe to decode non-production tokens

2. Production Tokens:
⚠️ Be cautious with production tokens
⚠️ Consider sensitivity of data
⚠️ Use on trusted devices only
⚠️ Clear after use

3. Sensitive Tokens:
✗ Avoid decoding on shared computers
✗ Don't decode during screen sharing
✗ Don't screenshot tokens

4. General Security:
✓ Use HTTPS (always)
✓ Use updated browser
✓ Keep browser extensions minimal
✓ Use private mode for sensitive operations

What Makes JWT Readable:

JWT is designed to be readable by anyone:
- Header: Base64URL encoded (easily decoded)
- Payload: Base64URL encoded (easily decoded)
- Signature: Verifies integrity (doesn't encrypt)

This means:
- Any JWT decoder (online or offline) can read your token
- Anyone with your JWT can decode it
- The signature prevents modification, not reading
- Never put secrets in JWT payload

Comparison with Other Decoders:

This Tool:
✓ 100% client-side
✓ No data transmission
✓ Open source
✓ Works offline
✓ No tracking

Some Other Tools:
✗ May send data to servers
✗ May log tokens
✗ May use analytics
✗ May require internet

Always check:
- Read privacy policy
- Check network activity
- Verify source code
- Test offline functionality

Recommendation:

For maximum security:
1. Use local JWT libraries for development
2. Decode tokens programmatically
3. Don't share tokens unnecessarily
4. Use short expiration times
5. Implement token refresh
6. Never commit tokens to version control

For this tool specifically:
✓ Safe for development use
✓ Safe for learning
✓ Safe for debugging
✓ Data never leaves your browser
✓ No tracking or logging

But remember:
- JWT payload is readable by design
- Signature prevents tampering, not reading
- Be cautious with what's in your tokens
- Follow general security practices

Conclusion:

Your token is safe with this tool because all processing is local. However, remember that JWT tokens are designed to be readable by anyone who has them. The signature ensures they can't be modified, not that they can't be read. Always follow JWT best practices and never put truly sensitive data (passwords, credit cards, etc.) in JWT payloads.

If you're concerned about privacy:
1. Use this tool on your personal, secure device
2. Use for development/test tokens only
3. Clear browser data after use
4. Or use local JWT libraries instead of online tools

Key Features

• Decode JWT tokens instantly
• View header (JOSE header) with algorithm and token type
• View payload with all claims and custom data
• View signature (base64url encoded)
• Automatic detection of standard JWT claims (iss, sub, aud, exp, nbf, iat, jti)
• Human-readable timestamp formatting for date claims
• Token expiration status checker
• Support for all JWT algorithms (HS256, HS384, HS512, RS256, RS384, RS512, ES256, ES384, ES512, PS256, PS384, PS512)
• JSON syntax highlighting and formatting
• Claims information section with detailed explanations
• Copy decoded parts to clipboard
• Download decoded output
• Upload JWT files for decoding
• Dark mode support
• 100% client-side processing - tokens never leave your browser
• Works offline after initial load
• No token size limits
• Mobile-friendly responsive design
• Clear error messages for invalid tokens
• Educational information about JWT security
• No registration or login required