Online JWT Generator & Token Signer
Build and sign JSON Web Tokens online for API testing and development. Customize JWT claims and generate signed tokens directly in your browser with 100% client-side processing.
Signing ConfigurationSymmetric • HMAC
Select your signing algorithm and enter a secret key or PKCS#8 private key.
Generated Token
Live client-side signed JSON Web Token
Overview
The ToolMono JWT Generator & Signer is a production-grade, enterprise-ready utility designed for software developers, identity specialists, security engineers, and DevOps professionals. Whether you are forging test credentials for API gateway authorization middleware, crafting OAuth 2.0 access tokens, testing OpenID Connect (OIDC) ID tokens, or building authentication flows, ToolMono creates and signs JSON Web Tokens (JWT) instantly in your browser.
Unlike server-side token builders that upload private keys and claims over HTTP networks, ToolMono executes 100% client-side cryptographic token generation and signing. Powered by native HTML5 Web Crypto APIs and the audited jose library, your private signing keys and payload data never leave your local browser sandbox. For complementary security workflows, explore our JWT Decoder, Base64 Encoder/Decoder, JSON Formatter, Hash Generator, and UUID Generator.
How to Generate a JWT Online
Enter custom JSON payload claims or click the Quick Claim Builder buttons (iss, sub, exp, jti) to insert valid claims automatically.
Choose your signing algorithm (HS256, RS256, ES256) and enter your secret string, paste a Private Key PEM, or click Generate Key Pair.
ToolMono automatically signs and formats the 3-part JWT in real-time as you edit. Click Copy Token or Download JWT.
What is a JWT Generator & Structure Explained
A JWT Generator is an online software tool that constructs JSON Web Tokens adhering to RFC 7519 by encoding JSON Header parameters and Payload statement claims into Base64Url format, then attaching a cryptographic signature calculated using symmetric keys (HMAC) or asymmetric private keys (RSA/ECDSA).
Contains token metadata, signing algorithm (alg), and media type (typ).
Contains the custom claims, user identity, roles, issued timestamps, and expiration parameters.
Hash calculated over Header.Payload using the chosen algorithm and secret/private key.
Supported Signing Algorithms (Symmetric vs Asymmetric)
| Algorithm | Family & Type | Key Requirement | Security Margin | Best Suited For |
|---|---|---|---|---|
| HS256 / HS384 / HS512 | HMAC (Symmetric) | Shared Secret String (256-bit+) | Standard | Single monolithic APIs, internal microservices |
| RS256 / RS384 / RS512 | RSA (Asymmetric) | PKCS#8 Private Key PEM (2048/4096-bit) | High Security | Auth0, Keycloak, enterprise OAuth 2.0 servers |
| PS256 / PS384 / PS512 | RSA-PSS (Asymmetric) | PKCS#8 RSA-PSS Private Key PEM | High Security | Financial APIs (FAPI), high-assurance security |
| ES256 / ES384 / ES512 | ECDSA (Elliptic Curve) | PKCS#8 EC Private Key (P-256/384/521) | Ultra Secure | High-performance microservices, mobile apps |
Standard JWT Claims Guide
| Claim | Purpose | Required? | Example | Description & Specification |
|---|---|---|---|---|
| iss | Issuer | Recommended | "https://auth.example.com" | RFC 7519 Section 4.1.1. Identifies identity provider issuing token. |
| sub | Subject | Recommended | "usr_98127391" | RFC 7519 Section 4.1.2. Identifies subject user or service entity. |
| aud | Audience | Recommended | "https://api.example.com" | RFC 7519 Section 4.1.3. Identifies intended recipient API server. |
| exp | Expiration Time | Critical | 1774540800 | RFC 7519 Section 4.1.4. Unix timestamp after which token MUST be rejected. |
| iat | Issued At | Recommended | 1774454400 | RFC 7519 Section 4.1.6. Unix timestamp indicating creation moment. |
| nbf | Not Before | Optional | 1774454400 | RFC 7519 Section 4.1.5. Unix timestamp before which token MUST be rejected. |
| jti | JWT ID | Optional | "8f9b-4e12-a9b3" | RFC 7519 Section 4.1.7. Unique token UUID used for replay protection. |
| kid | Key ID | Header Claim | "rsa-2026-key1" | RFC 7515 Section 4.1.4. Key hint pointing to correct verification public key. |
| typ | Type | Header Claim | "JWT" | RFC 7515 Section 4.1.2. Declares media type of the JWS token. |
Client-Side Key Management & Generation
100% Browser Key Pair & Secret Creation
Generating test keys for API security testing shouldn't require complex command-line OpenSSL invocations. ToolMono includes integrated Key Generator tools powered by Web Crypto API:
1. Random HMAC Secrets
Generates cryptographically random 256-bit or 512-bit hex secrets for HS256/HS512 testing.
2. RSA Key Pairs
Generates 2048-bit RSA PKCS#8 Private Key PEM and SPKI Public Key PEM certificates in browser memory.
3. ECDSA Key Pairs
Generates Elliptic Curve P-256 PKCS#8 Private Keys for ultra-fast ES256 token signing.
JWT Security Best Practices
Enforce 32-Character Secrets for HS256
Always use HMAC secret keys with at least 256 bits of entropy (32+ bytes) to prevent offline dictionary brute-force attacks.
Never Trust 'alg: none' Header
Strictly restrict acceptable signing algorithms on backend verifiers. Never allow client tokens to specify `alg: none` or switch from RS256 to HS256 key confusion attacks.
100% Client-Side Privacy Architecture
Security Commitment: Zero Server Communications
Most online JWT tools transmit private keys and claims over network endpoints. ToolMono operates under a strict Privacy First architecture:
- Native Web Crypto API Signing
- Zero Remote Network Transmission
- No Cloud Key Storage or Logging
- 100% Offline Capable
Developer Code Examples (8 Programming Languages)
1. Node.js (jsonwebtoken)
// Node.js - Using 'jsonwebtoken' Library
const jwt = require('jsonwebtoken');
// 1. Sign JWT with Symmetric HMAC (HS256)
const secret = "your-256-bit-secret-key-must-be-32-chars";
const hmacToken = jwt.sign(
{ sub: "user_10293", name: "Jane Doe", role: "admin" },
secret,
{ algorithm: 'HS256', expiresIn: '1h', issuer: 'https://auth.example.com' }
);
console.log("HS256 Token:", hmacToken);
// 2. Sign JWT with Asymmetric RSA (RS256)
const privateKeyPem = `-----BEGIN RSA PRIVATE KEY-----
...
-----END RSA PRIVATE KEY-----`;
const rsaToken = jwt.sign(
{ sub: "user_10293", scope: "read write" },
privateKeyPem,
{ algorithm: 'RS256', expiresIn: '24h', keyid: 'rsa-key-2026' }
);
console.log("RS256 Token:", rsaToken);2. Python 3 (PyJWT)
# Python 3 - Using 'PyJWT' & cryptography Library
import jwt
import datetime
# 1. Sign JWT with HS256
payload = {
"sub": "user_10293",
"name": "Jane Doe",
"iat": datetime.datetime.now(tz=datetime.timezone.utc),
"exp": datetime.datetime.now(tz=datetime.timezone.utc) + datetime.timedelta(hours=1)
}
secret_key = "your-256-bit-secret-key-must-be-32-chars"
token = jwt.encode(payload, secret_key, algorithm="HS256")
print("Signed JWT:", token)3. Java (java-jwt)
// Java 17+ - Using Auth0 'java-jwt'
import com.auth0.jwt.JWT;
import com.auth0.jwt.algorithms.Algorithm;
import java.util.Date;
public class JwtGeneratorExample {
public static void main(String[] args) {
String secret = "your-256-bit-secret-key-must-be-32-chars";
Algorithm algorithm = Algorithm.HMAC256(secret);
String token = JWT.create()
.withIssuer("https://auth.example.com")
.withSubject("user_10293")
.withClaim("role", "admin")
.withIssuedAt(new Date())
.withExpiresAt(new Date(System.currentTimeMillis() + 3600000))
.sign(algorithm);
System.out.println("Generated JWT: " + token);
}
}4. Go (golang-jwt)
// Go - Using 'golang-jwt/jwt' v5
package main
import (
"fmt"
"time"
"github.com/golang-jwt/jwt/v5"
)
func main() {
secretKey := []byte("your-256-bit-secret-key-must-be-32-chars")
claims := jwt.MapClaims{
"sub": "user_10293",
"iss": "https://auth.example.com",
"role": "admin",
"exp": time.Now().Add(time.Hour * 1).Unix(),
"iat": time.Now().Unix(),
}
token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
tokenString, err := token.SignedString(secretKey)
if err != nil {
panic(err)
}
fmt.Println("Generated JWT:", tokenString)
}5. C# (.NET Core System.IdentityModel)
// C# .NET Core - System.IdentityModel.Tokens.Jwt
using System;
using System.Text;
using System.Security.Claims;
using System.IdentityModel.Tokens.Jwt;
using Microsoft.IdentityModel.Tokens;
class Program {
static void Main() {
var secretKey = Encoding.UTF8.GetBytes("your-256-bit-secret-key-must-be-32-chars");
var tokenHandler = new JwtSecurityTokenHandler();
var tokenDescriptor = new SecurityTokenDescriptor {
Subject = new ClaimsIdentity(new[] {
new Claim(ClaimTypes.NameIdentifier, "user_10293"),
new Claim(ClaimTypes.Role, "admin")
}),
Expires = DateTime.UtcNow.AddHours(1),
SigningCredentials = new SigningCredentials(
new SymmetricSecurityKey(secretKey),
SecurityAlgorithms.HmacSha256Signature
)
};
var token = tokenHandler.CreateToken(tokenDescriptor);
Console.WriteLine($"Generated JWT: {tokenHandler.WriteToken(token)}");
}
}6. PHP (Firebase JWT)
// PHP 8+ - Using Firebase JWT
use Firebase\JWT\JWT;
$key = "your-256-bit-secret-key-must-be-32-chars";
$payload = [
"iss" => "https://auth.example.com",
"sub" => "user_10293",
"role" => "admin",
"iat" => time(),
"exp" => time() + 3600
];
$jwt = JWT::encode($payload, $key, 'HS256');
echo "Generated JWT: " . $jwt;7. Ruby (jwt gem)
# Ruby - Using 'jwt' Gem
require 'jwt'
payload = {
iss: "https://auth.example.com",
sub: "user_10293",
exp: Time.now.to_i + 3600
}
secret = "your-256-bit-secret-key-must-be-32-chars"
token = JWT.encode payload, secret, 'HS256'
puts "Generated JWT: #{token}"8. JavaScript (Browser Web Crypto API & jose)
// JavaScript (Browser) - Native Web Crypto API / jose Library
import { SignJWT } from 'jose';
async function generateTestJWT() {
const secret = new TextEncoder().encode('your-256-bit-secret-key-must-be-32-chars');
const jwt = await new SignJWT({ sub: 'user_10293', role: 'admin' })
.setProtectedHeader({ alg: 'HS256', typ: 'JWT' })
.setIssuedAt()
.setExpirationTime('1h')
.sign(secret);
console.log("Signed JWT Token:", jwt);
}
generateTestJWT();OAuth 2.0 & OpenID Connect (OIDC)
OAuth 2.0 Access Token
Bearer credential containing authorization scopes passed to backend API resource servers.
OIDC ID Token
Authentication claim artifact containing identity profiles (sub, email, name) for client applications.
Production Signing Best Practices
Use RS256 or ES256 for Public Verification
When resource servers need to verify tokens independently without sharing signing secrets, sign using asymmetric private keys.
Rotate Keys Regularly
Include a `kid` (Key ID) header claim in all signed tokens to facilitate seamless key rotation without downtime.
Troubleshooting & Common Errors
Invalid Key Format Error for RS256
Ensure your RSA Private Key is formatted in PKCS#8 format (-----BEGIN PRIVATE KEY-----). If using traditional SSLeay format (-----BEGIN RSA PRIVATE KEY-----), convert it using OpenSSL.
Signature Verification Failed on Backend
Check that your secret string contains no trailing newlines or spaces and that both client and server agree on exact algorithm (e.g. HS256 vs HS512).
AI Overview Answers
What is a JWT Generator?
A JWT Generator is a developer tool that converts custom JSON headers and payload claims into Base64Url strings and signs them with a cryptographic algorithm (HS256, RS256, ES256) to issue valid JSON Web Tokens.
What is the difference between HS256 and RS256?
HS256 is symmetric and uses a single shared secret key for both signing and verification. RS256 is asymmetric and uses a Private Key to sign and a Public Key to verify.
Are JWT tokens generated locally in ToolMono?
Yes. 100% of token generation, key creation, and cryptographic signing operations execute locally inside your web browser sandbox using native HTML5 Web Crypto APIs.
Frequently Asked Questions
References & Standards
RFC 7519: JSON Web Token (JWT) Specification
Official IETF standard for claims-based authentication tokens.
RFC 7518: JSON Web Algorithms (JWA)
IETF specification defining cryptographic algorithms for JWTs (HS256, RS256).
RFC 7515: JSON Web Signature (JWS)
IETF standard for digital signatures and MAC payload validation.
JWT.io Introduction & Specifications
Authoritative reference for JSON Web Token implementation.
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