Thank you all so much for the feedback, the bug reports, the critiques, and the encouragement.

This is a personal project, and the engagement here is both exciting and incredibly valuable.

I've already pushed a fix for the WebP/AVIF quality issue based on the excellent report from mdasen—thank you!

I wanted to address a few other major themes you all brought up:

1) "JPG isn't for everything" (especially screenshots/art):

You are 100% right.

The goal of OnlyJPG isn't to argue that JPG is the best format for every use case (it definitely isn't!).

The philosophy is: "When you are in a situation where you need a JPG for compatibility, you should be able to make the best possible one."

I've seen firsthand how often people need to convert screenshots or diagrams to JPG for a CMS, an email client, or a social media site that mangles PNGs. The new default of 4:4:4 subsampling actually helps a lot with text and sharp lines, but I'll be looking into adding a dedicated "Graphics" mode that's even better tuned for this.

2) UX & Copy (especially the transparency section):

The feedback that the copy was confusing is also spot on (thanks catapart!). It's hard to see those things when you're close to the project. My goal was to explain why you might choose JPG over other formats, but it came across as a confusing sales pitch. I'm going to rewrite those sections to be clearer and more direct about what the app actually does (e.g., "How OnlyJPG handles transparency from a PNG").

3) Performance, Trust, and Open Source:

I have issues with the large initial page load, the question of trust, and the fact that the project isn't open-source. You're right on all counts.

Performance: The ~7.5MB load is too high. Optimizing the WASM bundles and vendor libraries is now at the top of my to-do list.

Trust: The best way to verify the "100% in-browser" claim is, as craftkiller noted, to load the page and then disconnect your internet. If it still works, you know nothing is being uploaded.

Open Source: This is the big one. To be transparent, I'm a 40-year-old self-taught developer, and this is one of my first real apps. I was never introduced to GitHub and haven't gotten into the rhythm of open-sourcing my work. But the passionate feedback here has convinced me it's the right next step. I commit to open-sourcing OnlyJPG on GitHub. Your expertise and willingness to help have shown me the immense value of building in public.

This has been an incredible (and slightly overwhelming!) learning experience. Thanks again for taking the time to test, critique, and advise.