Software Factory

A prompt hands an agent one instruction and waits for you. A loop hands the agent a job, a way to know when the job is done, and a rule for when to give up — then runs the full cycle on its own until the goal is met. This skill is how we design loops that survive production instead of billing you in silence.

Call the concept by its older name: this is the software development lifecycle. A "loop" is one control-flow primitive inside a larger AI developer workflow — the plan → build → test → review → ship pipeline engineers used to walk by hand, now staffed by agents and deterministic code with an engineer at exactly two points: the plan going in (prompting is planning) and the review coming out (validation). Everything between those two constraints is system. The skill is named for the whole factory, with the iterate-until-verified loop as its engine — design the whole workflow, and remember the highest-leverage work is building the system that builds the system — the agentic layer, where one improvement multiplies across every future run.

The single most important idea: the gate is the loop. Without a real, automated check on the result, you don't have a loop — you have an agent agreeing with itself on repeat. Everything else (scheduling, sub-agents, connectors) is plumbing around that one load-bearing part. Design the gate first.

Three actors: code, engineers, agents

Every workflow node is staffed by one of three actors, and reliability ranks them code > engineers > agents. Code runs deterministically at zero token cost and never hallucinates; agents are the most expensive and least reliable actor in the system. The placement heuristic: push every deterministic step — lint, format, typecheck, test runs, status updates, result routing — into plain code, and reserve agents for the judgment steps code can't do. Staffing an agent where code suffices is the most common way loops burn money. The corollary for gates: run checks as separate code, feed failures back to the maker agent in the same session, and never bury the whole ladder inside one mega-skill the agent interprets (see failure modes).

The five building blocks

Every production loop is assembled from these five. Claude Code ships all of them.