CLI coding agent
A CLI coding agent is a command-line program that lets a model read, run and edit things in a working directory, under whatever approval rules you set.
Claude Code and Codex CLI are the two in common use. Both run in a terminal, both work against the repository you are standing in, and both are driven by a subscription rather than requiring an API key.
The terminal matters more than it sounds. It is where the code, the tests and the version control already are, so the agent needs no integration layer to act on real state.
It also means the cost profile is the agent one rather than the chat one: tool calls, accumulated results, and a transcript that is re-sent on every turn.