NoobCoder-208/FixOb54JWT — reverse-engineered prompt

Build me a small Python app for troubleshooting JWT tokens that I can deploy on Vercel. I want something simple and usable, either a basic web page or a lightweight API, where I can paste a token and quickly see if it is valid, expired, malformed, or missing expected claims. It should clearly decode the header and payload, explain common errors in plain English, and make it obvious what needs to be fixed.

Please keep the setup minimal and make sure it actually works with a Vercel Python deployment. If there is already a starting point in app.py, use that and clean it up rather than overbuilding. Add any small helper pages or responses needed so a normal person can test it in the browser and also with requests.

Keep the code straightforward, with sensible error handling and a short note on how to run it locally and deploy it. If you need to, look up the current Vercel Python docs online.