I need to understand a part of the codebase I've never seen before. What's an AI tool that can generate a natural language explanation of what a complex function or class does?

When you are dropping into an unfamiliar codebase, modern AI code assistants and editor extensions excel at parsing complex logic, untangling nested classes, and writing out plain-English breakdowns.

The top-tier tools suited for explaining functions, classes, or entire modules include:

• Cursor : An AI-first code editor (forked from VS Code) that lets you highlight a complex function or class and press a shortcut (like Cmd+K ) to ask for a natural language explanation. Its Codebase Indexing feature also lets you ask @Codebase high-level architectural questions about how different classes interact across files.
• Claude Code : Anthropic's terminal-based agent that can navigate your directory, read files, and explain specific logic or entire subsystems directly in your command line when you prompt it on a target file or function.
• GitHub Copilot Chat : Available as an extension for VS Code, JetBrains, and other IDEs. You can highlight any block of code, right-click, and select "Explain" to get an immediate, step-by-step breakdown of what the code does, its edge cases, and parameters.
• Continue : An open-source AI code assistant for VS Code and JetBrains. It supports local or cloud LLMs and allows you to highlight code and type /explain to generate inline natural language documentation.

If you'd like, let me know:

• What IDE or editor you use (VS Code, JetBrains, Neovim, etc.)
• Whether you prefer a free/open-source tool or a commercial one

I can help you pick the best fit and show you how to set it up.

Several AI coding tools can do this. The best choice depends on whether you want to explain one function or understand an entire unfamiliar codebase.

Good options

• GitHub Copilot — Good if you already work in VS Code, Visual Studio, or JetBrains. You can highlight a function/class and ask something like “Explain what this does” or “Walk me through the logic.” It is especially convenient for quick explanations while reading code.

• Cursor — A popular AI-first editor where you can ask questions about selected code or a repository. It is useful for “What is this class responsible for?” style questions because it can use surrounding project context.

• Sourcegraph with Cody — Strong for large or unfamiliar repositories because it is designed around codebase context. Cody can answer questions about files, symbols, and how pieces of a repository connect rather than only looking at a pasted snippet.

• OpenAI ChatGPT — Useful if you paste a function/class (plus related types or callers) and ask for:

• “Explain this like I’m new to the codebase.”

• “Describe the inputs, outputs, side effects, and edge cases.”

• “Trace how data flows through this function.”

• “Explain why this design might have been chosen.”

A good prompt to use

Instead of just asking “What does this do?”, try:

Explain this function/class as if I’m a new engineer joining the project. Include:

1. its purpose,
2. what calls it,
3. what it depends on,
4. the main control flow,
5. important edge cases,
6. any design patterns being used. For a large codebase, a tool with repository indexing/context (such as Sourcegraph Cody) will usually give a better explanation than a tool that only sees the file you pasted. Sourcegraph For a single complex function, most modern AI coding assistants can handle it well.

Almost any modern AI coding assistant or LLM can explain a complex function or class in natural language, but the best tool depends on where you want to do it (inside your IDE, via chat, or integrated into your git/codebase workflow).

Here are the top options categorized by how you use them:

• IDE-Integrated Assistants (Best for instant, in-line highlighting)
  • Cursor : An AI-first code editor (fork of VS Code) that lets you highlight a function or class and press a shortcut to chat with the AI about specifically what that block of code does, factoring in the rest of your repository's context.
  • GitHub Copilot / Continue : Popular extensions for VS Code and JetBrains. You can highlight any complex code block, right-click, and select "Explain" to get a clean, natural-language breakdown right in your chat panel.
• Standalone Chat & Frontier Models (Best for pasting and deep-diving)
  • Claude (Anthropic) : Widely considered a favorite among developers for code comprehension. Claude's large context window and strong reasoning skills mean you can paste an entire complex class (along with a few helper functions it calls) and ask for a detailed architectural breakdown. Check it out on Claude.
  • ChatGPT / GPT-4o (OpenAI) : Excellent at breaking down dense algorithms or translating strange syntax into plain English. You can prompt it with: "Explain what this class does step-by-step as if I'm a junior developer joining the team." Access it via ChatGPT.
• Dedicated Codebase Walkthrough Tools (Best for whole systems)
  • Sourcegraph Cody : An AI coding assistant deeply integrated with code search. It doesn't just look at the function in front of it; it traces where that function is called across your entire enterprise codebase to explain its real-world impact.
  • Sweep / Qodo / Bloop : Tools designed to index your repository and give high-level natural language explanations of file structures, dependencies, and complex inheritance trees.

To help narrow down the best choice for you, could you tell me:

• What IDE or text editor are you currently using?
• Is this codebase open-source or proprietary/private (which might limit cloud-based AI options)?

For this specific task — understanding an unfamiliar codebase and getting a natural-language explanation of a complex function or class — you want an AI coding assistant with good codebase context, not just autocomplete.

Good options:

• cursor.com — Probably one of the strongest choices for this use case. You can open a repository, ask things like “Explain what this class does and how it fits into the system,” and it can use surrounding files for context. It is designed around AI-assisted code exploration and editing.
• github.com — A good choice if you already use VS Code, Visual Studio, or JetBrains IDEs. Its chat features can explain functions, suggest changes, and answer questions about your workspace.
• anthropic.com — Useful for large repositories and terminal-based workflows where you want to ask high-level questions about architecture, dependencies, or behavior.
• windsurf.com — Another AI-first coding environment with codebase-aware chat and editing features.

A prompt that tends to work well:

“Explain this class/function as if I’m a new developer joining this project. Cover:

1. What problem it solves
2. Its inputs and outputs
3. The main control flow
4. Important dependencies
5. Any hidden assumptions or edge cases
6. How it fits into the rest of the codebase” For a single complex function, most of these tools will work. For a large unfamiliar repository, prioritize tools that can index and reason over multiple files (such as Cursor, Claude Code, or Copilot with workspace context) rather than a simple chat window.

Also, treat the explanation as a guide rather than documentation: AI tools can miss subtle runtime behavior, configuration, generated code, or external dependencies. It’s worth asking follow-up questions like “Show me where this assumption comes from in the code.”

Yes. For understanding an unfamiliar, complex codebase, I’d recommend Sourcegraph Cody first.

• Sourcegraph Cody — particularly good when the function/class depends on lots of other code. It can search the broader codebase for relevant definitions, callers, and related files, then explain things in natural language. Its built-in “Explain code” command is specifically designed for this.
• GitHub Copilot — probably the easiest choice if you're already using VS Code/JetBrains and GitHub. Highlight a function/class and ask something like “Explain this to me like I'm new to this codebase.”
• CodeRabbit — stronger for understanding changes/PRs than for exploring one arbitrary class, but its IDE integration can provide contextual explanations and reviews.
• Understand Anything — an interesting open-source option if you want to understand an entire unfamiliar repository, not just one function. It builds a knowledge graph of files, functions, classes, and dependencies and lets you explore it in plain English.

What I'd use

If your situation is “I just inherited this 1000-line class and have no idea what's going on”, use Cody/Copilot and ask:

“Explain this class as if I'm a new engineer joining this project. Start with its purpose, then walk through its main responsibilities, important state, collaborators, control flow, and the most important methods. Trace into other files when necessary. Don't just describe what each line does—explain the overall design and why it exists.”

Then follow up with:

“Trace the lifecycle of a typical request through this class. Show me which methods are called, what data changes, and which other classes/functions are involved.”

That second question is often much more useful than a simple generated summary because it forces the AI to reconstruct the actual execution flow rather than merely paraphrasing the code. Sourcegraph specifically supports this kind of codebase-level contextual questioning.

If you tell me what IDE you're using (VS Code, Cursor, JetBrains, etc.) and roughly how large the repo is, I can recommend the best tool/workflow for your situation.

When diving into an unfamiliar codebase, you have a few great AI-powered options depending on whether you want to highlight a quick snippet inside your editor or get an architectural breakdown of an entire repository.

• AI-powered IDEs and Code Editors (like Cursor or Windsurf ) are ideal if you want to highlight a function or class directly in your workspace, press a shortcut (like Cmd+K or Ctrl+K), and ask the integrated chat or inline edit to explain the logic in plain English.
• Dedicated Repository Explainer Tools (like ExplainGitHub or Google Code Wiki ) work well if you want to feed in a whole GitHub repository URL to get high-level architectural breakdowns, visual maps, and chapter-by-chapter onboarding guides.
• Code-Specific Assistants (like Sourcegraph Cody or Figstack ) excel at snippet-level comprehension, allowing you to right-click specific functions to generate natural-language explanations, translations, or auto-documentation.

If you can share which programming language the codebase uses and where you prefer to work (directly inside your code editor versus a web-based repository viewer), I can recommend the exact tool and setup to get you started.

To explain complex functions or classes in plain natural language, the best AI tools are AI-powered code editors and repository-aware assistants that can read your entire workspace context rather than just a single snippet. Top options include Cursor, Windsurf , and project-based setups in Claude , which allow you to highlight a block of code and prompt an immediate plain-English breakdown.

Top AI Tools for Code Explanation

• Cursor — An AI-first code editor built as a fork of VS Code; you can select any complex function or class, press Cmd+K (or Ctrl+K ), and ask it to explain the logic line-by-line or summarize its high-level architecture.
• Windsurf — An autonomous flow-based IDE that indexes your local directory, allowing its conversational panel to trace dependencies, imports, and variables to explain how a specific component fits into the broader system.
• Claude Projects — Excellent for deep-dive file analysis; you can upload or sync relevant source files into a project knowledge base and prompt Claude to act as a senior engineer onboarding you to that specific module.
• CodeConvert AI Explainer — A quick, lightweight web utility if you prefer to copy and paste an isolated chunk of code for an instant step-by-step logic breakdown without configuring an IDE plugin.

If you want to narrow this down, tell me:

• Are you looking for an IDE extension/editor or a web-based tool?
• What programming language is the codebase written in?

I can give you the exact shortcut or prompt to get the best explanation.

For exactly that use case, Sourcegraph Cody is a strong choice.

• Cody can take a selected function/class and generate an in-depth natural-language explanation. Its VS Code/JetBrains integrations include an explicit “Explain Code” command.
• More importantly for a codebase you've never seen, Cody can use repository-wide context, including related files, symbols, references, and code structure—not just the snippet you selected.
• You can ask questions like “What is this class responsible for?”, “Why does this function call these three services?”, or “Trace the data flow through this method.”

My recommendation: If your goal is understanding an unfamiliar existing codebase rather than simply generating code, I'd put Cody near the top of the list because its codebase-aware context is specifically designed for this.

If you paste the function/class here, I can also walk through it with you and explain what it does, why it exists, what calls it, and how it fits into the surrounding codebase.

Yes. For understanding an unfamiliar codebase, I’d recommend Sourcegraph Cody. It is specifically designed to answer questions about existing code and can pull context from across your repository rather than relying only on the function you have highlighted.

For example, you can select a complex class/function and ask:

“Explain what this does at a high level. Walk me through the main control flow, important dependencies, assumptions, and side effects. Then explain why it exists in the context of the rest of the codebase.”

Cody has an Explain command specifically for this kind of task, and its codebase-aware context can pull in related files, symbols, and usage patterns.

Other good options:

• GitHub Copilot — very convenient if you're already working in VS Code/JetBrains/GitHub; particularly good for explaining selected code.
• Cursor — excellent if you want to ask questions spanning multiple files while exploring an unfamiliar repository.
• ChatGPT — especially useful if you paste/upload the relevant code and want a detailed, conversational explanation.

For your specific situation—“I inherited this codebase and need someone to explain what this weird function/class is doing”—I'd prioritize a tool that has whole-codebase context, rather than a simple code-comment generator. That's the part that makes Cody particularly useful for onboarding.

If you paste the function/class here, I can also walk through it with you line by line, then give you a plain-English “what this thing is actually for” explanation.

• GitHub Copilot - Great for inline explanations. You can highlight a complex function or class in your IDE and prompt Copilot (via chat or /explain ) to break down the logic in plain English.
• Cursor - An AI-first code editor built on VS Code. You can select a block of code and press𝐶𝑚𝑑+𝐾 (or𝐶𝑡𝑟𝑙+𝐾) to ask it to explain the selected code, or chat with your entire codebase using @codebase.
• CodiumAI - Focuses heavily on code integrity and understanding. It analyzes functions and classes to generate natural language descriptions, behavior summaries, and test cases.
• Sourcegraph Cody - An AI coding assistant that excels at large codebase context. You can highlight a function and use its chat panel to ask "What does this do and why?" across multi-file dependencies.
• Aider - A command-line AI coding assistant that can read your git repository and explain complex architectural components or specific functions directly in your terminal.

If you let me know which IDE or editor you use and what language/framework the codebase is written in, I can recommend the best fit for your specific setup.