CoreCoder
A roughly 1,300-line, fully readable coding-agent engine meant as a teaching reference for how a tool like Claude Code actually works, so a developer can read the whole thing and fork it into something of their own.
CoreCoder is a minimal AI coding agent, formerly called NanoCoder, with a 1,309-line engine inside 2,658 total lines of Python, meant to be read end to end in an afternoon with no hidden magic. It strips a coding agent down to its essential parts: a loop wrapped around a large model plus a small set of tools that let it read, edit and run code, and deliberately keeps only that minimal core so a developer can set a breakpoint on any line, change it, and rerun it on their own machine.
It works with any LLM rather than one specific provider, and its growth since an original 1,161-line snapshot has gone into visible, addable features such as plan mode, hooks and checkpoints, each documented in an accompanying series of bilingual essays that read through the source. The README compares its size and readability against Claude Code and aider, positioning itself as the foundation a developer stands on while learning from larger tools, not a competing production assistant.
It is written in Python.