JWT Generator / Signer
LiveCreate and sign JSON Web Tokens with custom claims, headers, and HS256/RS256 algorithms.
Understanding JWT Token Creation
Creating JWTs is essential for implementing authentication systems, testing API authorization flows, and generating access tokens during development. A JWT generator constructs tokens by combining a header (specifying the signing algorithm), a payload (containing claims like user identity, roles, and expiration), and a cryptographic signature. In production, JWTs are created by authentication servers after verifying user credentials, but during development you often need to generate test tokens with specific claims to simulate different user scenarios, roles, and token states.
Create JSON Web Tokens with custom header and payload claims. Sign with HMAC-SHA256 (HS256) using a secret key. Set standard claims like iss, sub, aud, exp, iat, and add custom fields. Complements the JWT Decoder for full JWT workflow.
The Devkitr JWT Generator creates signed JSON Web Tokens from custom header and payload configurations. Choose a signing algorithm, define claims in the payload editor, set expiration and other standard claims, and generate a valid JWT. The tool supports HMAC symmetric signing for development testing and displays the complete token alongside its decoded structure for verification.
In a typical development workflow, JWT Generator / Signer becomes valuable whenever you need to create and sign json web tokens with custom claims, headers, and hs256/rs256 algorithms. Whether you are working on a personal side project, maintaining production applications for a company, or collaborating with a distributed team across time zones, having a reliable browser-based generation tool eliminates the need to install desktop software, write one-off scripts, or send data to third-party services that may log or retain your information. Since JWT Generator / Signer processes everything locally on your device, your data stays private and your workflow stays uninterrupted — open a browser tab, paste your input, get your result.
Key Features
Custom Claim Editor
Define any combination of standard (sub, iss, aud, exp, iat) and custom claims in a JSON editor with syntax validation before token generation.
Algorithm Selection
Choose between HS256, HS384, and HS512 HMAC algorithms for symmetric signing, matching the algorithm configured in your application's token verification.
Expiration Controls
Set token validity duration with preset options (1 hour, 24 hours, 7 days, 30 days) or custom Unix timestamp for precise expiration control.
Instant Token Decode Display
Shows the generated token alongside its decoded header and payload, so you can verify the contents match your configuration before using the token.
How to Use JWT Generator / Signer
Configure the Header
Select the signing algorithm (HS256 is standard) and optionally set additional header fields like kid (key ID) if your verifier requires it.
Define the Payload Claims
Enter claims in the JSON editor — sub (subject), iss (issuer), aud (audience), exp (expiration), roles, permissions, and any custom data.
Set the Signing Secret
Enter the shared secret key that your application uses for HMAC verification. The same key must be used on the verifying server.
Generate and Copy
Click generate to produce the signed JWT. Copy the token for use in Authorization headers, test scripts, or API client configurations.
Use Cases
Local Development Authentication
Generate JWTs with specific user IDs and roles to test different authentication scenarios without running a full auth server locally.
Testing Role-Based Access Control
Create tokens with different role claims (admin, editor, viewer) to verify your API enforces authorization rules correctly for each role.
Expired Token Testing
Generate tokens with past expiration timestamps to test that your application properly rejects expired tokens and triggers refresh flows.
Integration Test Fixtures
Create pre-signed test tokens with known claims for automated integration tests that validate authentication middleware behavior.
Pro Tips
Use a strong, random secret key for HMAC signing — at least 256 bits (32 bytes) of random data. Short or predictable secrets can be brute-forced.
Always include mandatory claims (iss, sub, exp, iat) even in test tokens — this builds good habits and catches claim validation issues early.
Test with tokens that have different aud (audience) claims to verify your verifier rejects tokens intended for other services.
Generate tokens with nbf (not before) claims set in the future to test that your application properly handles tokens that are not yet valid.
Common Pitfalls
Using weak secrets like "secret" or "password" for JWT signing
Fix: Use a cryptographically random secret at least 256 bits long. Weak secrets allow offline brute-force attacks that compromise all tokens signed with that key.
Putting sensitive user data (email, SSN, credit card) in JWT payloads
Fix: JWT payloads are Base64-encoded, not encrypted — anyone with the token can read the claims. Store only identifiers and metadata, not sensitive personal data.
Creating tokens without expiration (exp) claims
Fix: Tokens without expiration are valid forever, creating persistent security risks if compromised. Always set reasonable expiration times (1-24 hours for access tokens).
Frequently Asked Questions
QWhich signing algorithms are supported?
HMAC-SHA256 (HS256) is supported for client-side signing. This is the most common algorithm for symmetric JWT signing.
QCan I set expiration times?
Yes. Set the exp (expiration) claim using a duration picker or enter a specific Unix timestamp.
QHow does this work with the JWT Decoder?
Generate a token here, then use the JWT Decoder to verify the contents. Together they provide a complete JWT development workflow.
QIs my secret key sent anywhere?
No. Signing happens entirely in your browser. Your secret key never leaves your device.
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