JWT Builder
Construct and sign JWT tokens online for free. Our JWT builder lets you define a custom header and payload JSON, choose a signing algorithm (HS256, RS256, ES256, and more), and generate a signed token instantly — all in your browser with no signup required.
Construct a signed JWT token from a custom header and payload JSON with your signing secret or private key. All signing happens locally in your browser — nothing is sent to any server.
Why Use Our JWT Builder?
Instant JWT Construction
Build and sign JWT tokens in milliseconds directly in your browser. Our JWT builder processes header and payload JSON instantly with no server round-trips or upload delays.
Secure JWT Builder Online
Your secrets and private keys never leave your device. The JWT builder uses the browser-native Web Crypto API for all signing operations — 100% client-side and completely private.
JWT Builder Online — No Installation
Use the JWT builder directly in any modern browser without installing libraries, SDKs, or command-line tools. Works on any OS with no plugins or extensions required.
Multiple Algorithm Options
Choose from 9 signing algorithms — HS256, HS384, HS512 for symmetric HMAC tokens, RS256/RS384/RS512 for RSA asymmetric tokens, and ES256/ES384/ES512 for ECDSA elliptic-curve tokens.
Common Use Cases for JWT Builder
API Development & Testing
Generate test JWT tokens with custom claims to simulate authenticated API requests during development without spinning up a full identity provider.
Auth Flow Prototyping
Prototype OAuth and OIDC authentication flows by constructing tokens with specific issuer, audience, and scope claims to validate your authorization logic end-to-end.
Security Testing
Build tokens with edge-case claims — expired timestamps, missing fields, or unusual algorithms — to test how your backend handles malformed or adversarial JWT inputs.
CI/CD Pipeline Tokens
Create short-lived service-to-service JWT tokens for CI pipeline authentication, enabling secure machine-to-machine communication without long-lived credentials.
Learning & Education
Understand JWT structure hands-on by building tokens with different algorithms and inspecting the Base64URL-encoded header, payload, and signature segments side by side.
Microservice Authorization
Craft tokens with custom role and permission claims to test microservice authorization policies and validate that your middleware correctly enforces access control rules.
Understanding JWT Construction
What is a JWT Builder?
A JWT builder is a tool that constructs JSON Web Tokens (JWTs) from a header and payload JSON object, then signs the result using a cryptographic key. JWTs are compact, URL-safe tokens defined in RFC 7519 and widely used for authentication and authorization in web APIs, microservices, and OAuth/OIDC flows. Our JWT builder online tool lets you construct and sign tokens entirely in your browser without any server-side processing.
How Our JWT Builder Works
- 1. Input Your Header and Payload: Paste or edit the header and payload JSON objects. The JWT builder automatically sets the
algandtypfields in the header based on your selected algorithm. - 2. Instant Browser-Based Signing: Click "Build JWT" and the tool signs your token using the Web Crypto API directly in your browser. Your secret or private key is never transmitted to any server.
- 3. Copy or Download the Token: The signed JWT token appears in the output field. Copy it to your clipboard or download it as a text file. The individual Base64URL-encoded segments are also shown separately.
What Gets Included in the JWT
- Header: Contains the token type (
typ: "JWT") and the signing algorithm (alg), Base64URL-encoded as the first segment. - Payload: Contains your custom claims such as
sub,iss,exp, and any application-specific fields, Base64URL-encoded as the second segment. - Signature: A cryptographic signature over the header and payload using your chosen algorithm and key, Base64URL-encoded as the third segment.
- Final Token: The three segments joined by dots —
header.payload.signature— forming the compact JWT string ready for use in Authorization headers.
Important Security Notes
JWT tokens built with this tool are cryptographically signed but not encrypted. The header and payload are Base64URL-encoded and readable by anyone — do not include sensitive data like passwords or PII in JWT payloads. Always validate tokens server-side and enforce issuer, audience, and expiry checks in production systems.
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Frequently Asked Questions About JWT Builder
A JWT builder is a tool that constructs JSON Web Tokens from a header and payload JSON object and signs them with a cryptographic key. Our JWT builder online tool lets you create signed tokens for HS256, RS256, ES256, and other algorithms entirely in your browser — no signup required.
No. Our JWT builder processes everything locally using the browser-native Web Crypto API. Your shared secret or private key PEM is never sent to any server or third-party service. The signing operation runs entirely on your device.
Absolutely. All JWT construction and signing happens client-side in your browser. No token data, secrets, or private keys are uploaded to external servers. This makes the JWT builder safe to use even with sensitive development credentials.
Yes. Our JWT builder is 100% free with no hidden costs or limitations. No signup required, no premium tier, no usage limits, no file size restrictions, and no advertisements.
The JWT builder supports all three major algorithm families: HMAC symmetric algorithms (HS256, HS384, HS512) using a shared secret; RSA asymmetric algorithms (RS256, RS384, RS512) using a PKCS#8 private key PEM; and ECDSA elliptic-curve algorithms (ES256, ES384, ES512) using a PKCS#8 private key PEM.
The JWT builder expects private keys in PKCS#8 PEM format — the format that starts with "-----BEGIN PRIVATE KEY-----". If your key is in PKCS#1 format ("-----BEGIN RSA PRIVATE KEY-----"), you can convert it using OpenSSL: openssl pkcs8 -topk8 -nocrypt -in key.pem -out key_pkcs8.pem.
Yes. The payload editor accepts any valid JSON object, so you can include standard registered claims (sub, iss, aud, exp, nbf, iat, jti) as well as any custom application-specific claims your API requires.
HS256 uses a symmetric shared secret — the same key signs and verifies the token, making it suitable for single-service scenarios. RS256 uses an asymmetric RSA key pair — the private key signs the token and the public key verifies it, which is better for distributed systems where multiple services need to verify tokens without access to the signing secret.
Yes. Use our JWT Debugger & Signature Verifier tool to decode and verify any JWT token you build here. Paste the token and provide the same secret or public key to confirm the signature is valid and inspect all claims.