Page 5 of 8~120 min topic

Function calling in code

Debug executing a hallucinated tool name in the order-status tool caller

Page 5 reproduces and repairs the characteristic failure of the order-status function-calling assistant: executing a hallucinated tool name, or answering status without a tool call.

~15 min this pageDebugging

1Learn the idea

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Reproduce before you repair

Do not start with a speculative fix for the order-status tool caller. Force the failure on purpose, save the before output, then change one cause at a time. Retries are allowed only for transient conditions—not for bad input that will fail forever on function-calling-code.

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Force the failure

for (let attempt = 0; attempt <= maxRetries; attempt++) {
  try { return await operation(signal); }
  catch (error) {
    const failure = classify(error);
    if (!failure.retryable || attempt === maxRetries) throw failure;
    await sleep(jitteredBackoff(attempt), signal);
  }
}
throw new Error("unreachable");

Expected evidence: A request for ord_123 produces one validated lookup and a reply based only on its result.. If you cannot reproduce on demand, you do not yet control the failure mode for function-calling-code.

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Repair with a reviewable diff

After repair, rerun the exact reproduction command. Keep the failing fixture as a regression seed for the observability page. For the order-status function-calling assistant, remember the claim you are restoring: when the model emits a valid tool call, the runtime executes only the allowlisted function.

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Lab notebook: reproduce on command

Store a one-command reproduction for: executing a hallucinated tool name, or answering status without a tool call. The command should use orders map + tool schema for get_order_status or a minimal mutant of it. Paste the failing output into notes/failure-before.txt (or your shell scrollback as copied text). After the fix, paste notes/failure-after.txt and keep both.

Retries belong only on transient faults. If the failure is bad input, a bad allowlist, or a logic bug in the order-status tool caller, retrying will amplify cost without repairing trust around let the model request a read-only get_order_status tool, then answer from the tool result.

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Worked judgment

Classify the failure as prevent, detect, contain, or recover—using this lab’s language, not a generic poster. For function-calling-code, the first fix should usually be detect+prevent at the boundary, because executing a hallucinated tool name, or answering status without a tool call is cheaper to stop early than to explain in production prose.

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Why this stage matters for the order-status tool caller

At the debugging stage for function-calling-code, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about orders map + tool schema for get_order_status that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: assistant that answers without tools on the same prompts.

For this page specifically, success looks like before/after evidence for the characteristic failure while still centering the user decision to let the model request a read-only get_order_status tool, then answer from the tool result. If you cannot point to a file, command, or assertion that proves that for the order-status tool caller, stay on this page instead of advancing.

Glossary: tool · Glossary: structured output · Cheatsheet: production ops signals

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Before you start

Why this matters

Describe the smallest fixture that triggers executing a hallucinated tool name. Predict the first visible symptom (exception, wrong label, silent empty success). You will compare that prediction with the reproduction below.

In the wild

See how this idea shows up as a product and a company — then come back to the lesson. Skills transfer across vendors.

Check your understanding

Page assessment

Answer from memory. Completion is saved from this evidence, not from opening the next page.

1. Can you reproduce the failure with a one-command fixture?
2. Did you avoid retrying non-transient bad input?
3. Is before/after evidence saved as text (not only a screenshot)?
4. Does the repair restore the metric path toward: tool-call validity rate?

All responses are required.