Hi HN,

Whenever I needed an LLM to reliably output JSON or follow strict formatting rules, I kept having to write throwaway JavaScript scripts just to test the same prompt against OpenAI, Anthropic, and Google APIs to see who actually followed the instructions. It was a tedious workflow, so I built a local desktop UI to just do it for me.

What it does:

* Sends one prompt to OpenAI, Anthropic, Mistral, and Google simultaneously so you can compare the outputs in a single grid.

* Automatically checkpoints your runs. If you tweak a word and the output gets worse, you can just click back to the previous version.

* Exposes raw API responses, latency stats, and token usage instead of hiding them behind a chat UI.

* Saves your history to a local SQLite file on your disk.

* Keeps your API keys encrypted locally (zero telemetry).

Yes, it is built on Electron. I sincerely apologize to your RAM. I tried to mitigate the usual bloat by sticking to vanilla JS and native Web Components, so it idles around ~240MB, but it definitely still has some rough edges.

My plan is a one-time $29 perpetual license, but right now the public beta is completely free. I'm holding off on charging because I need a solid Merchant of Record to handle global tax compliance. Lemon Squeezy seems appropriate, but I still need to validate it (sadly, Stripe isn't onboarding new customers from India right now). If anyone has recently dealt with a payment processor that handles global compliance for desktop software, I would really appreciate your suggestions.

You can grab the Mac, Windows, or Linux binaries here: https://aptselect.com/

If this fits into your workflow, I'd love to hear your feedback, bug reports, or any features you'd actually want in a local prompt runner.

Show HN: AptSelect – A local desktop app to test LLMs side-by-side