Explain Diff HTML — Development skill for Claude Code

Explain Diff (HTML)

A Claude Code skill that turns a code change into one self-contained HTML page that teaches a reader what changed and why.


Why this exists

AI is helping us write code faster than ever.

That's great, but there's also a side effect: we're generating more code, reviewing bigger changes, and sometimes understanding less of what actually happened.

You open a PR and suddenly there are hundreds, maybe thousands, of changed lines across a bunch of files.

Git shows you the diff file by file.

`controller.ts`

`service.ts`

`utils.ts`

tests...

But that's usually not how the change actually works.

So where do you start?

Which file matters first? What calls what? Why was the change needed? How does the data move through the system?

And that's where PR reviews can start becoming difficult.

For me, PRs have always been one of the best ways to learn a codebase. You look at someone else's changes, follow the flow, understand why they made certain decisions, and slowly build a better mental model of the system.

As AI generates more of the implementation and PRs keep getting larger, I didn't want to lose that learning opportunity.

That's where **explain-diff-html** came from.

Instead of explaining a change in the order Git happens to show the files, it tries to follow the **logical flow of the code**.

So instead of:

`file A → file B → file C`

it might explain it as:

`request → handler → service → transformation → result`

It looks at the diff, the surrounding code, callers, related definitions, commits, and documentation, then turns all of that into a walkthrough that tries to answer a simple question:

**"If I actually want to u