JWT ES256 Generator

This tool generates a compact JWT signed with ES256 from a user supplied header and payload and a PEM encoded EC private key. It adheres to JOSE and JWT standards and is designed for developers, security engineers, and QA teams needing test tokens for API authentication, OAuth flows, and service to service calls. Tokens are produced locally and are not stored. The tool accepts a JSON header and payload and produces a single token in the header.payload.signature form.
Conceptually, the workflow builds the signing input as the base64url encoding of the header, followed by a dot, then the base64url encoding of the payload. It signs this input using ECDSA with SHA-256 on the P-256 curve and encodes the resulting signature in base64url format. The final string is suitable for use in Authorization headers or token exchange flows. The tool enforces ES256 as the signing algorithm and validates that the private key corresponds to the P-256 curve. It supports common claims such as iss, sub, aud, exp, nbf, and iat, and allows optional kid in the header. The token generation is deterministic for the same inputs and does not rely on external services.
The unique value lies in strict ES256 enforcement, PEM input validation, and RFC 7515/7519 compliant output, making it reliable for testing real world authentication scenarios. It is useful for API clients, microservice authentication tests, and CI pipelines that require authentic tokens without exposing service secrets.
Use cases include API token generation for secure endpoints, testing token validation logic, and validating JWT-based access control during development and QA.