Debugging Tool Loops

Debugging tool loops

Symptom: agent makes 8+ tool calls (often repeating searches with slight variations), eventually hits stepCountIs(10) cap or runs out of output tokens, ends with output: {response: ""} or empty complete args.

Diagnostic checklist

1. Confirm the loop signature

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describe_session(sessionId) → session.agentBlocks[].toolCalls

Look for:

• 6+ tool calls in a single agent block.
• Repeated calls to similar tools (search_issues × 3, search_pull_requests × 3, then more search variations).
• No complete or failStep toolName in the list.
• Final assistant text is empty.

If the agent IS calling complete but with empty args, that's @friday/debugging-empty-output step 2, not this skill.

2. Check the agent prompt's termination criterion

A loop usually means the agent doesn't know when to stop searching. Look for prompts like:

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"Search for all stale issues across all repos."

The LLM keeps searching because "all" is open-ended. Add an explicit stop condition:

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"Search exactly these 6 queries (3 issue queries × 3 PR queries).
After all 6 return, stop and call `complete` with the report. Do not
search again."

3. Check whether the agent has the right terminal tool

If outputTo is set, the runtime auto-injects complete and stops the LLM when complete is called (stopWhen: hasToolCall("complete")). If outputTo is NOT set, the LLM stops only on stepCountIs(...) or max output tokens. Without an outputTo, you're at the mercy of the LLM's own sense of when to stop.

Consider adding outputTo: response to the FSM action to give the LLM a clear exit hatch.

4. Bump max_steps only as a last resort

The default max_steps: 10 is generous for most agents. If you genuinely need more (e.g., a job that fans out to 20 repos), bump it in the action's config.max_steps. But: if you're hitting 20 steps and still not done, the prompt is wrong, not the budget.

What NOT to do

• Do NOT bump max_output_tokens to "fix" the loop. Token budget isn't the issue — the agent isn't producing tokens, it's producing tool calls. More budget = more loops.
• Do NOT swap to a more capable model. Tool loops aren't a model capability problem; they're a prompt instruction problem.

Cross-references

• @friday/debugging-broken-jobs — the triage entry point.
• @friday/debugging-empty-output — sibling for "complete present but empty" cases.
• @friday/agent-action-handshake — the outputTo + complete injection contract that gives a terminal exit.