Why One Simple Loop Drives Every Coding Agent

Wed, 02 Sep 2026 09:30:00 +0000

I read the Gemini CLI source code for a concrete reason: last year I built a Code Agent product internally, and while designing its loop mechanism I wanted to see how an open-source implementation already running on many developers’ terminals actually does it. So I went through the Gemini CLI core directories.

The conclusion surprised me: the essential thing is tiny — it’s a loop. The model speaks, fires tool calls, receives tool results, and speaks again. Everything else — approvals, context compression, loop detection, budget control, model fallback — is peripheral engineering built around that loop. Even the question of “who speaks next” is just a decision point inside the loop: when the model finishes a line without firing any tool, a lightweight model gets asked once whether to continue or hand control back, and “continue” simply starts another turn.

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Why One Simple Loop Drives Every Coding Agent