Curl Source Code Explorer: Learn a 30-Year-Old Codebase Without Getting Lost
Curl has been running on virtually every computer on the planet for nearly three decades. The project started in 1996 as a small tool called httpget, was renamed curl in March 1998, and has been quietly powering downloads, API calls, and network requests ever since — making it one of the most widely deployed pieces of software ever written.
It’s one of the most-used pieces of software ever written — and almost nobody who uses it daily has ever read a line of its source code. That’s partly because diving into a mature C codebase is intimidating. There are no onboarding docs for the internals, no guided tour, no one to ask why a particular function was written the way it was. You’re either grepping through 170,000 lines alone, or you’re not reading it at all.
I built a small browser app to fix that.
Tool description
The app lets you pick a module — the DNS resolver, the TLS handshake, the cookie engine, the HTTP redirect logic — and step through its key functions one by one. For each concept, you get the actual source code side-by-side with an AI-generated explanation tuned to your experience level. A complete beginner gets plain-English analogies. An experienced C programmer gets architecture notes, edge cases, and the tradeoffs baked into the implementation.
It also tracks your progress. You mark concepts as understood or flagged for review, jot notes directly on each function, and quiz yourself when you want to test retention. Everything persists locally across sessions.
The whole thing runs in the browser with no installation. Drop two files in a folder, spin up a local server, paste a free Groq API key, and you’re reading curl internals with an expert looking over your shoulder.
It won’t replace reading the code yourself — and it’s honest about that. Every snippet has a direct link to the live GitHub file, with a clear disclaimer that the embedded code is a snapshot and curl commits almost daily. The goal isn’t to replace the source. It’s to make the source approachable enough that you actually open it.
Built with React, Groq (Llama 3.3 70B), and real curl source from github.com/curl/curl.
Prompt Used:
Create a webapp to read and understand the source code of Curl package. I should be able to track my learning progress and also review my understanding of the key concepts and file level functioning. Also provide a way to track progress, review notes and revisit lesser understood concepts.
I should be able to select level of difficulty, length of source code and key modules.