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?

Yes. For this specific use case, Sourcegraph Cody is a strong fit. It can take the surrounding codebase into account—not just the function you highlighted—and answer questions about functions, classes, symbols, callers, and how pieces fit together. Sourcegraph specifically describes Cody as using codebase context and search to help developers understand code.

You could highlight a function and ask:

“Explain what this function does in plain English. Start with its purpose, then walk through the major steps, important inputs/outputs, side effects, and any other functions it depends on. Assume I'm unfamiliar with this codebase.” Other good options:

• GitHub Copilot — convenient if you're already working in GitHub/VS Code and want an explanation directly alongside the code.
• Claude Code — particularly useful when you want to ask questions spanning multiple files rather than just explain one function.
• Understand Anything — a more specialized option that builds a knowledge graph of files, functions, classes, and dependencies and provides plain-English explanations; it has commands specifically for deep-diving into a function or module.
• CodeRabbit — useful if your goal is understanding code in the context of reviews and changes; it supports conversational questions about reviewed code.

For a codebase you've never seen before, I'd prioritize a tool that can see repository-wide context, rather than a generic “paste this function into ChatGPT” workflow. That lets you ask follow-ups like “Why is this called here?”, “Where does this data come from?”, and “What happens after this returns?” without manually gathering all the relevant files.

If you tell me your IDE (VS Code, IntelliJ, Cursor, etc.) and language, I can suggest the most convenient option and give you a prompt that produces a really good code walkthrough.

Cursor is an AI-first code editor built specifically for this purpose, letting you highlight any complex function or class and instantly generate a natural language explanation or chat directly with your codebase.

Top AI Tools for Code Explanation

• Cursor : An AI code editor (forked from VS Code) with deep codebase indexing. You can use shortcut keys (Ctrl+K or Cmd+K ) on a highlighted block of code or use Ctrl+L / Cmd+L to chat and ask it to explain what a specific class or function does in plain English.
• Claude Projects (Anthropic) : Excellent for deep textual analysis. You can upload or drag-and-drop entire folders or files of a repository into a project and prompt Claude to break down complex logic or design patterns.
• GitHub Copilot Chat : Directly integrated into your IDE (VS Code, JetBrains), allowing you to highlight a function, right-click, and select "Explain" to get a real-time conversational breakdown in your sidebar.
• Sourcegraph Cody : An AI coding assistant that uses large-scale code graph context to explain whole systems, map out dependencies, and describe what unfamiliar functions do across large enterprise codebases.

What IDE or text editor are you currently using for your development workflow?

GitHub Copilot, Cursor , and standalone AI chat assistants are the most effective tools for generating natural language explanations of complex functions or classes.

Modern AI code assistants integrate directly into your editor or workspace to read surrounding context, dependencies, and project architecture, translating complex logic into plain English.

Top AI Tools for Code Explanation

• GitHub Copilot Chat : Highlight any complex function or class inside your IDE (VS Code, JetBrains, Visual Studio), open the chat panel, and use /explain to get a structured breakdown of what the code does, how data flows through it, and edge cases it handles.
• Cursor IDE : An AI-first fork of VS Code that indexes your entire codebase. You can use command-K on a specific block of code or reference entire files in chat (@filename ) to get deep, context-aware explanations of how a class fits into the broader system architecture.
• Sourcegraph Cody : An AI coding assistant built specifically for large-scale enterprise codebases. It uses deep code search and a large context window to explain unfamiliar repositories, functions, and inter-file dependencies accurately.
• General AI Chatbots (ChatGPT / Claude) : Copy and paste the specific function or class along with its immediate helper functions into ChatGPT or Claude and prompt it to explain the logic step-by-step. Note: This lacks automatic repository context, so you must manually provide necessary type definitions or imports.

Best Practices for Prompting Code Explanations

When asking an AI to explain unfamiliar code, use specific framing to avoid vague summaries:

1. Ask for data flow : Prompt the tool to trace inputs through the function's logic gates and state changes.
2. Request an analogy : Ask the AI to compare the function's behavior to an everyday process if the underlying algorithm is abstract.
3. Identify side effects : Explicitly ask what external states, global variables, or databases the function or class modifies.

If you tell me what programming language and IDE or editor you use, I can give you the exact keyboard shortcut or setup steps for the best tool in your workflow.

Yes. For this specific task, I’d recommend GitHub Copilot Chat or Sourcegraph Cody.

• GitHub Copilot Chat — probably the easiest if the project is already on GitHub. It can use repository context and explain a specific function, class, file, data flow, or architecture. GitHub specifically documents using it to understand unfamiliar codebases and individual symbols.
• Sourcegraph Cody — my pick if the function depends on lots of other files/classes. Cody can retrieve relevant code from across the codebase rather than just looking at the selected snippet, which makes it particularly useful for complicated or unfamiliar systems.

A prompt that works well

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

Explain this function/class as if I'm a new developer joining this project. Start with its purpose, then explain the control flow step by step, important inputs/outputs, dependencies on other parts of the codebase, and any non-obvious design decisions. End with a short plain-English summary of when and why this code is used. For a really complex function, I'd use Cody or Copilot iteratively: first ask for the high-level purpose, then ask it to trace the important calls and data flow. That tends to produce a much more useful explanation than asking for one giant summary.

If you tell me what IDE you're using (VS Code, IntelliJ, Cursor, etc.), I can recommend the best tool for that setup and give you a ready-to-paste prompt.

Yes. For understanding an unfamiliar, complex codebase, I’d start with Claude Code or Cursor.

• Claude Code — probably my first choice for a complicated function/class because it can reason across the surrounding repository, not just the snippet. It’s particularly strong when understanding requires tracing callers, dependencies, types, tests, and related files.
• Cursor — excellent if you want to stay inside an IDE and ask conversational questions such as “What does this class do?”, “Why is this method called here?”, or “Trace this data from the API to this function.” Its codebase-aware workflow is particularly convenient for iterative exploration.
• GitHub Copilot — a good choice if you're already using VS Code/GitHub. It handles individual function explanations well, although comparisons suggest it may need more explicit prompting for deeper whole-repository analysis.

A prompt that works well

Give the tool the function/class and ask:

Explain this code as if I'm a new engineer joining the project. Start with the purpose in plain English, then explain the control flow step by step. Identify important inputs/outputs, dependencies, side effects, error handling, and assumptions. Then trace where this function is called and what calls it. Point out anything non-obvious or potentially dangerous. Don't suggest changes yet—I just want to understand it. For a really complex class, add:

Also explain its role in the larger architecture and identify the 3–5 other files I should read next to understand it. That last instruction is particularly useful: instead of getting a generic line-by-line explanation, you get a reading path through the unfamiliar codebase.

If you tell me what editor/language you're using (e.g. VS Code + Python, IntelliJ + Java, etc.), I can recommend the best tool and exact workflow for your setup.

To understand a complex or unfamiliar part of a codebase, several modern AI tools specialize in reading code and generating clear, natural language explanations:

• GitHub Copilot Chat : Integrated directly into your IDE (VS Code, JetBrains), you can highlight a complex function or class and ask it to /explain what the code does step-by-step.
• Cursor : A fork of VS Code built entirely around AI. It lets you use Cmd+K or Chat to reference entire files or codebases, offering deep context-aware architectural and functional explanations.
• Cody (by Sourcegraph) : Excellent for larger, multi-repository codebases. It can analyze deep call hierarchies and explain how a specific function or class interacts with the rest of the system.
• Continue : An open-source AI code assistant that plugs into VS Code and JetBrains, allowing you to connect local or cloud LLMs to highlight and document/explain legacy functions.
• Aider : A command-line tool that lets you bring an LLM directly into your git repository to chat about, explain, and refactor specific code blocks in your terminal.

If you want, I can:

Compare GitHub Copilot Chat vs. Cursor for code explanation Give you a prompt template to get the best explanation from an AI tool Explain how to set up an open-source alternative locally

When diving into an unfamiliar codebase, you don't just want a tool that looks at a single line—you need something with full repository context that can trace dependencies, inputs, and side effects.

The top-tier AI tools for generating natural language explanations of complex functions, classes, or entire modules include:

• Cursor: An AI-first code editor (forked from VS Code) that lets you highlight a function or class and use shortcut commands (like Ctrl+K or Cmd+K ) to ask for a plain-English breakdown. Its "Codebase Indexing" feature allows you to chat with your entire repo, asking questions like "What does this class depend on and how does it process user authentication?"
• GitHub Copilot Chat: Integrated directly into standard IDEs like VS Code and JetBrains. You can highlight any complex snippet, open the chat panel, and use /explain to get a structured, step-by-step description of what the logic accomplishes and why.
• Claude Code / Claude (Anthropic): Excellent for deep-dive architectural analysis. You can point Claude Code via the terminal or paste complex blocks into Claude's interface and ask it to break down the logic "like a senior engineer explaining it to a teammate", detailing hidden edge cases and state transformations.
• Sourcegraph Cody: Built specifically with large-scale codebases in mind. Cody uses semantic code search and deep graph context to explain how a local function interacts with remote services, database models, or other classes across the wider repository.

If you'd like to narrow this down, let me know:

• What IDE or text editor you prefer to use
• Whether your codebase is local or private/enterprise (impacting privacy/indexing preferences)

I can help you pick the best tool setup for your workflow.

If your goal is “I have a function/class I’ve never seen—explain what it does in plain English”, several AI coding tools are good at this:

• github.com — probably the easiest starting point if you already use VS Code, Visual Studio, or GitHub. You can highlight a function/class and ask things like:

• “Explain what this function does.”

• “Walk me through the control flow.”

• “What assumptions does this code make?”

• “Summarize this class for a new developer.”

Copilot Chat is designed to answer coding questions using code context and can help explain repositories, files, and components.

• cursor.com — an AI-first code editor that is useful when you need to understand a larger unfamiliar codebase. It can index a project so you can ask broader questions like “How does authentication work in this repo?” or “Where is this class used?”
• docs.anthropic.com — useful when the explanation requires understanding many files together. It works from the terminal and is designed for repository-level tasks, so it can help trace relationships between classes, modules, and dependencies.
• openai.com — useful for asking questions about code, getting explanations, and working through changes with an AI coding agent.
• github.com — a more specialized option for onboarding to large codebases. It builds a map of files, functions, classes, and dependencies, then provides plain-English summaries and exploration tools.

A good prompt to use with any of them:

“Explain this class as if I’m a new engineer joining the project. Describe its purpose, responsibilities, important methods, inputs/outputs, dependencies, and any surprising behavior.” For a single complex function, most tools above work well. For a large unfamiliar codebase, I’d lean toward Cursor, Claude Code, or a codebase-mapping tool because the hard part is usually understanding how pieces connect, not just what one function does.

Yes. Cursor is probably the best fit for exactly this use case.

• Cursor — Open your repository and use Ask mode. You can ask something like, “Explain what this class does, its responsibilities, its dependencies, and the important control flow.” Cursor can search the codebase and trace references rather than looking at the function in isolation.
• GitHub Copilot — Especially convenient if your code is already on GitHub. Copilot Chat can explain a selected function/class or use repository context to explain how pieces of the codebase fit together.

My pick: Cursor if you're trying to understand a complex, unfamiliar codebase, because it can trace related code and answer follow-up questions. Copilot is excellent if you're already working primarily inside GitHub/VS Code.

A useful prompt is:

“Explain this function like I'm a developer joining this project. First give me its purpose in plain English, then walk through the control flow, inputs/outputs, important side effects, dependencies, edge cases, and why it might have been designed this way. Also point me to the other functions/classes I should read to understand it fully.” That tends to produce much more useful explanations than simply asking “What does this function do?”

When jumping into an unfamiliar codebase, several AI-powered tools excel at breaking down complex functions, classes, or entire architectural flows into plain, natural language.

Top AI Tools for Code Explanation

• Greptile : Acts as an AI expert on your specific codebase. You can chat with it in Slack or via its web interface, ask "what does this function do?", and it will explain the logic while factoring in cross-file dependencies and how data flows through the system.
• Qodo (formerly CodiumAI) : Excellent for deep functional analysis. Integrated directly into your IDE, it can analyze specific blocks of code, classes, or functions to generate behavioral descriptions, identify edge cases, and even write tests to prove its understanding.
• CodeRabbit : While primarily built for AI-driven pull request reviews, it provides deep semantic breakdowns of code changes, making it easy to read what a newly introduced or complex function actually accomplishes in context.
• Cursor / VS Code with Copilot (Chat) : If you highlight a complex function or class in an IDE like Cursor or VS Code , you can use shortcut commands (like /explain ) to prompt an advanced LLM to walk through the logic line-by-line in natural language.
• Repo-level Map Tools (like Codemap or Sourcegraph Cody) : These tools index your entire repository to give AI a structural overview, allowing you to query specific classes and get high-level architectural summaries instead of isolated guesses.

If you'd like, let me know:

• Which IDE or workflow you prefer (VS Code, CLI, web-based)
• Whether you want a tool for one-off explanations or to index the whole repo

I can help you pick the best fit and show you how to prompt it effectively.