Code Explainer: Paste Any Code, Get a Plain-English Explanation
Paste any code and get a clear, plain-English explanation of what it does. The AI auto-detects the language, walks through the logic, and flags anything unusual or potentially buggy. Free, no account required.
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AI Code Explainer for Python, JavaScript, SQL, and More
Understanding unfamiliar code is one of the most time-consuming parts of software development. Whether you're onboarding to a new codebase, reviewing a pull request, or trying to understand what an AI generated, reading code without context is slow. Paste any snippet and get a structured, plain-English breakdown of exactly what it does - overview first, then logic block by block.
The AI auto-detects the language and gives an overview of purpose before walking through each section in detail. It flags bugs, potential issues, and anti-patterns after the explanation. For runtime errors in the code you just understood, use our Error Explainer. To generate tests for the code, our Unit Test Generator works directly from code you paste. For regex patterns found in the code, our Regex Generator can explain or rewrite them.
Languages Supported
When to Use a Code Explainer
Code explainers are most valuable in situations where you need to understand code you didn't write, quickly and accurately.
Understand unfamiliar functions and modules quickly without spending hours tracing execution paths manually.
Get a plain-English summary of what a PR does before you start reviewing, so you can focus on correctness rather than comprehension.
Reading code in a language you're learning is faster when you can ask for explanations of idioms and patterns you don't recognise.
When a function behaves unexpectedly, explaining it line by line often reveals the assumption that caused the bug.
Get a plain-English translation of what a piece of code does that you can share with product managers or stakeholders.
AI-generated code is often correct but opaque. Explaining it line by line before committing it is good practice.
How to Read Unfamiliar Code: A 4-Step Method
Experienced developers don't read code top to bottom like prose. They triangulate. The same method works whether you're reading manually or deciding what to paste into the explainer first.
Locate where execution actually starts: the main function, the route handler, the event listener, the exported public method. Everything else in the file exists to serve that entry point, so it anchors your mental model. In a web app, pick one request and follow it.
Ask "what shape is the input, and what shape leaves at the end?" Follow one variable through its transformations and ignore branches that don't touch it. Most functions become obvious once you know what their data looks like at each stage.
Codebases have dialects: get_ vs fetch_ vs load_ often distinguish cache reads from network calls from disk I/O. A leading underscore signals "internal, don't call directly". Learning the project's vocabulary early saves rediscovering it function by function.
Tests are executable documentation. A test named test_rejects_expired_token tells you a business rule no comment ever recorded. If there are no tests, the explainer's edge case notes serve the same role: they tell you what the code is supposed to guarantee.
Common Code Smells the Explainer Flags
A code smell isn't a bug. It's a structural hint that a bug will be easy to introduce later. These are the five the explainer calls out most often, and what each looks like in the wild.
| Smell | What it looks like | Why it matters |
|---|---|---|
| Long function | One function scrolling past 50-80 lines, doing validation, transformation, and persistence in a single body. | Impossible to test in isolation; every change risks an unrelated part of the same function. |
| Deep nesting | Four or more levels of if/for indentation forming an arrow shape down the screen. | Each level multiplies the paths through the code. Early returns and guard clauses flatten it. |
| Magic numbers | Bare literals like if retries > 3 or price * 1.21 with no named constant. |
The next reader can't tell whether 1.21 is VAT, a margin, or a typo, and can't safely change it. |
| Shotgun surgery | One conceptual change, like renaming a status value, requires edits in a dozen scattered files. | Signals that one concept has no single home. Sooner or later one of the dozen sites gets missed. |
| Duplicate logic | The same validation or calculation re-implemented in two places, already slightly out of sync. | Fixing a bug in one copy and not the other is how "we fixed that already" bugs are born. |
When you paste code that exhibits one of these, the explanation includes a Note: pointing it out, with a concrete suggestion rather than a lecture.