Developer uses Ed25519 public-key signing to enable offline licence checks in browser tool

A developer built a browser-based Bates-numbering tool for litigation PDFs that processes all files locally, never uploading documents to a server, to comply with legal confidentiality requirements. Because privileged legal documents may be subject to court protective orders restricting where they can travel, a traditional server-side licence validation system was not viable. Instead, the developer ships an Ed25519 public key directly in the JavaScript bundle and uses the browser's built-in WebCrypto API to verify licences entirely offline. Licence keys follow a custom format containing a base64url-encoded payload and signature, which are validated with a single crypto.subtle.verify call requiring no third-party cryptography library. The signing private key never leaves the developer's machine, meaning the scheme is secure even if the verification logic and public key are fully visible in the client-side bundle.