Natural language code explanation

If your main goal is “I’ve never seen this function/class before—explain what it’s doing in normal human language, including how it fits into the rest of the codebase,” the current tools are not equally good.

My shortlist

1. Cursor — probably the best fit

For your particular use case, I'd start here.

Cursor's documentation explicitly supports asking it to explain unfamiliar code, trace flows across a repository, and summarize large classes. For example, it demonstrates asking for the responsibilities and main methods of a 2,000-line PaymentGateway class. It can also generate diagrams showing how components interact.prod.cursor.com+1

What's particularly useful is that it doesn't just look at the function you're staring at. Its agent can search the repository semantically, follow references, inspect related files, and build an explanation from that context.prod.cursor.com+1

Cursor documentation on understanding unfamiliar code

A prompt I'd use:

Explain this class as if I'm a senior developer joining this project for the first time.
Start with its purpose in plain English. Then explain each responsibility, the important methods, what calls them, what they call, important state/invariants, and any non-obvious design decisions.
Don't just paraphrase the code—build me a mental model of how it fits into the application.

Then follow with:

Now trace one realistic request through this class from entry point to return value.

That second question is often where these tools become genuinely useful.

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2. Anthropic Claude Code — excellent for deep archaeology

I'd put Claude Code roughly alongside Cursor if you're willing to work from a terminal.

Its big advantage is that you can ask questions that require investigating many files rather than just explaining the currently open file. Independent 2026 comparisons have generally highlighted Claude Code's context handling and multi-file reasoning as a strength, although those evaluations are third-party rather than controlled benchmarks.www.sitepoint.com

It's particularly interesting when you encounter something like:

processRequest() makes no sense to me. Figure out what this function is actually responsible for. Trace every significant caller and dependency, then explain why it exists and what assumptions it makes.

That's more of a software archaeology task than an autocomplete task, and Claude Code is well suited to it.

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3. GitHub Copilot — surprisingly good for targeted explanations

Copilot is especially convenient when you're already looking at code on GitHub or working in VS Code.

GitHub explicitly supports asking Copilot to explain a specific function, class, symbol, file, directory, commit, or entire repository. It can ground the response in the repository's actual files and symbols rather than treating the selected code as an isolated snippet.docs.github.com

For example, you can select a symbol and ask:

Explain this symbol. What problem does it solve? Who calls it? What assumptions does it make? Explain the important branches without simply restating the code.

That's excellent for quick “what the hell is this?” moments.

GitHub's guide to exploring a codebase with Copilot

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4. OpenAI Codex — worth considering for repository-level investigation

Codex belongs in the same category as Claude Code and Cursor rather than old-school autocomplete: the important distinction is that these agents can search files, reason about relationships, and investigate a task rather than merely predict the next line.

For your use case, I'd evaluate it on how well it can answer questions requiring context outside the file you're viewing, rather than on autocomplete quality.

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The important distinction

For this particular task, I wouldn't primarily ask:

“Which AI has the smartest model?”

I'd ask:

“Which tool gives the model the best access to the codebase while making it easy for me to interrogate its understanding?”

That's why Cursor stands out. Its documentation specifically describes semantic codebase search, reference tracing, an Explore subagent, Ask mode, and architectural diagrams.prod.cursor.com+1

And there's a useful workflow:

1. Start broad

Give me a mental model of this subsystem.

2. Narrow down

Explain FooService and why it exists.

3. Trace

Show me what happens when FooService.process() is called.

4. Zoom in

Explain this 40