What is loop engineering?
Accuracy note: the people, dates, and figures in the origin story below are recorded as of June 2026 — verify before relying. Every external claim has a row in SOURCES.md.
Definition
Loop engineering is the practice of running an AI coding agent in a governed, verifiable loop until a clearly defined goal is met. Where prompt engineering shapes a single turn, loop engineering shapes the outer loop: what the agent does, how it checks its own work, when it stops, and what it costs.
A useful one-liner (Addy Osmani, as of June 2026 — verify before relying): loop engineering is "designing the loop the agent runs in, not just the prompt it runs once." See SOURCES.md.
Where the term came from
The idea predates the name. A short, labeled timeline (as of June 2026 — verify before relying; sources in SOURCES.md):
| When | Who | What |
|---|---|---|
| Jul 2025 | Geoffrey Huntley | popularized the bare "Ralph" loop — re-run the same prompt in a while true until done |
| Jun 2026 | Steinberger | a viral thread on running agents in long unattended loops |
| Jun 2026 | Boris Cherny | framing loops inside coding-agent tooling |
| Jun 2026 | Addy Osmani | named and defined "loop engineering" as a discipline |
| Jun 2026 | Greg Brockman | described a governed "Ralph loop++" |
The throughline: a one-shot prompt became a loop, and the loop grew governance (stop conditions, cost caps, verification) until it was worth treating as its own engineering surface.
Prompt → context → harness → loop
The four things you actually design, from innermost to outermost:
- Prompt — what to do on a single pass.
- Context — what the agent knows this pass (repo state, inputs, the source of truth). Fresh context each pass beats one ever-growing transcript.
- Harness — the tools, permissions, and memory the agent runs inside.
- Loop — repeat until a verifiable done-condition (or an interval fires), with governance around it.
Loop engineering is mostly about the outer two rings: the harness and the loop. The rest of this guide is how to design them.
Next: /goal vs /loop basics →