Show HN: I made a heatmap diff viewer for code reviews

Can someone please explain to me how do people build these kind of tools? My background is classic Java/C# backend development and SQL. A bit microservice using Spring Boot. Its 8:30pm and I'm watching React tutorials to understand better how modern websites are built - e.g. use useState, useRef etc.

Now, how does any of my experience translate to building tools like cmux? I genuinely want to understand how.

Is the answer to go line by line of cmux code base or make an attempt to open a PR on one of the bugs issues on cmux and, by magic and time, I will eventually understand?

What would you recommend to someone new in your team who had only ever used python and a bit of SQL, and had never touched Java or Spring Boot?

High level: hit github api, feed code to llm, display results in web app.

If you want to learn web apps start with the docs, eg. Official react docs or even just learning vanilla JavaScript if you don’t know it.

Start with little pieces like hitting the github API and displaying some json in the terminal

You could also just start prompting an llm to scaffold a project for you and then trying to debug whatever issues come up (and they will)

If your goal is to make something useful, I think the fastest way is probably to build a CLI only version since you can theoretically render heatmaps and make a task manager in a CLI form factor. And your background in Java/C# helps here.

Use Claude Code or Codex for everything, learn how to prompt well. >90% of cmux and 0github.com was written by LLMs. Most of it was just me asking the LLM to implement something, testing it to see if it works, and if it doesn't, I'll ask the LLM to write logs, and I'll paste the logs back to the LLM. Ask gpt-5-pro for architecture choices, like what tech/dependencies to use.

But if your goal is to learn React, I'd recommend going through the official getting started documentation, it's pretty good.

Your experience in coding is enough, you need more practice in "problem solving" with crazy ideas and working through them to the finish line.

Besides, this is just a thin layer on an LLM, with questionable actual quality. Learn to do the real work, no magic machine can take learning and skill building off your shoulders.

I suggest that you ask Claude Code to build such a website for you with a minimal set of features, with tons and tons of comments and design/architecture documents plus tests. Once that is done, you can start reading the code. You can even read as it is working.

Then, you can point Claude Code to a file/a function/a few lines and ask follow-up questions.

After that, there are even more things to do. If you want a different perspective, you could try completely reimplementing the thing. My guess is that Claude will use Next.js. You can ask Claude not to do that but instead use a different UI framework/no framework combined with C#, if that's something you are interested in. If you want to actually learn all the details, you can start setting things up yourself and write the website. You can add features or try making the site scalable, under AI-assisted or vibe coding mode.

It will not produce the most elegant code or have the best architecture, but will be good enough for your purpose. I think it's the most efficient way to get some learning that is specifically suited to your needs in this age.