Agent Loops

Most agent work is one-shot: a prompt goes in, an answer comes out. The next step in agentic systems is the loop — run a step over and over, letting the agent keep working until the goal is met instead of stopping after one pass. One agent improves an architecture while another removes duplicated abstractions, both opening pull requests continuously; a draft is refined until it’s good enough; a build is fixed and re-run until it’s green.

The catch is cost and runaway risk: a loop “burns through tokens a lot faster than a simple Q&A chatbot,” and a non-deterministic stop (“keep going until you’re done”) has no natural ceiling. So a usable loop needs two things:

a stop condition — how it decides it’s done, and
a hard cap — a guardrail that guarantees it always terminates.

Go Micro gives you both as a flow step: flow.Loop.

The shape

flow.Loop is a StepFunc, so it drops into a flow’s ordered, checkpointed step list like any other step. It runs a body step repeatedly, carrying the flow State from one pass to the next, until a stop condition fires or the iteration cap is hit — whichever comes first.

f := micro.NewFlow("refactor",
    micro.FlowProvider("anthropic"),
    micro.FlowSteps(
        micro.FlowStep{Name: "improve", Run: micro.FlowLoop(
            micro.FlowDispatch("coder"), // the body: an agent does one pass
            micro.FlowUntilLLM("Is the refactor complete with no duplicated abstractions left?"),
            micro.FlowLoopMax(5),        // the ceiling: never more than 5 passes
        )},
    ),
)

Stop conditions

Code-defined — FlowUntil stops when your predicate returns true. Use it when “done” is something you can measure (tests pass, a score clears a threshold, a queue is empty):

micro.FlowUntil(func(_ context.Context, s micro.FlowState, iter int) (bool, error) {
    var d Draft
    _ = s.Scan(&d)
    return d.Quality >= 90, nil
})

Model-judged — FlowUntilLLM asks the flow’s model, after each pass, whether the goal is met, and stops on an affirmative answer. This is the supervised (“Ralph”) loop: the agent decides when it’s done, while the cap still guarantees it stops. It requires a flow model (FlowProvider/FlowAPIKey).

micro.FlowUntilLLM("Have all the failing tests been fixed?")

You can combine both — either firing stops the loop.

The guardrail

FlowLoopMax(n) is the ceiling. The body never runs more than n times, so the loop always terminates even if the stop condition never fires. When the cap is hit, the loop returns the latest state rather than erroring — the guardrail did its job. Always set it. For tighter budgets, keep the cap low and pair the loop with agent guardrails (e.g. token/spend limits) and paid tools (per-call metering) so a background loop can’t run up an unbounded bill.

Watching progress

FlowOnIteration runs after each pass — log it, or persist a summary so you can see how a long-running loop is doing:

micro.FlowOnIteration(func(iter int, s micro.FlowState) {
    log.Printf("pass %d: %s", iter, s.String())
})

Durability

A loop runs as a single flow step. The flow checkpoints the loop’s outcome (before and after the step) through its Checkpoint, and a resume re-enters the step — so keep loop bodies safe to repeat. For long loops, use FlowOnIteration to persist per-pass progress.

Run it

A complete, offline example (no API key — the body and stop condition are plain Go) is in examples/flow-loop:

go run ./examples/flow-loop/
# refining until quality >= 90
#   pass 1 → quality 30
#   pass 2 → quality 60
#   pass 3 → quality 90
# done: {"text":"draft refined (quality 90)","quality":90}

Swap the body for micro.FlowDispatch("agent") or micro.FlowLLM(...) and the stop check for micro.FlowUntilLLM(...) to turn it into a real agent loop.