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Designing Reliable Planning Loops

Build reliable thought-action-observation cycles that let agents decompose complex goals into executable steps without going off-track.

By Amit UpadhyayPublished 20 MayUpdated 06 Aug 202612 minArticle 3 of 12 in Agentic Systems

A goal goes to a loop chooser that picks ReAct, Plan-and-Execute or ReWOO; a planner writes steps, an executor runs them, and a replanner checks progress until the answer is synthesised.

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The idea at a glance

The problem

When

An agent must carry out a task of ten or more steps

The obvious move

A ReAct loop that decides every step with the whole history in the prompt

Fails because

Each step resends everything so far, so cost grows with the square of the step count, and long loops drift away from the goal

The fix

Planning loops works by

Choosing the loop by the task: plan-and-execute for mostly predictable work, with a validated plan, cheap execution steps and re-planning only on failure

At the cost of

A plan schema and validation step, and less flexibility when the task turns out to be unpredictable

The scenario every mode follows

“Migrate tenant acme-co from us-east to eu-west.”

A data-migration agent that moves a customer’s account between regions: export, verify, transfer, re-index, switch DNS, confirm
~30 migrations a week
gpt-6-1-sol

Where the obvious approach breaks

12 steps ≈ 6.5× the tokens of planning once

If you run every step through a ReAct loop with the full history.

If each step adds about 1,500 tokens and the full history is resent, step k sends k × 1,500 tokens: 12 steps send 1,500 × (1 + 2 + … + 12) = 117,000 tokens. Planning once and executing each step with only its own inputs sends about 18,000.

Helps to know firstAgent design patterns

How the Agent Decides What to Do Next

A single LLM call is good at one-shot reasoning; it is bad at multi-step tasks where intermediate state matters. Planning loops give the agent an explicit plan, execute the steps, observe results, and revise. The choice of planning loop — ReAct, Plan-and-Execute, ReWOO, Reflexion — is the single biggest lever on latency, cost, and reliability of an agent.

If your agent runs long tasks

Your ReAct agent burns 30 LLM calls to answer a 3-step question
You picked a planner but can't articulate why it's the right one
Your agent never recovers from a tool failure — it just retries forever

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