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A watchdog for an AI coding agent belongs in the host application that runs the agent’s tool loop. Set a finite run budget there, watch for repeated actions and lack of verified progress, and decide in advance whether hitting a limit stops the run or pauses it for review. The available facts do not establish the author’s programming language, harness, thresholds, implementation, or test results, so this article explains a practical design rather than claiming a specific system was built or measured.

Where an agent loop happens

In a client-tool workflow, the model proposes a tool call; the host application executes it and sends the result back to the model. The host then decides whether to make another model request. Anthropic’s tool-use documentation describes this cycle: “In practice this reads as: while stop_reason == "tool_use", execute the tools and continue the conversation.” The application must handle other stop reasons rather than treating every response as permission to continue. Anthropic’s tool-use documentation

That boundary is the most dependable place for a watchdog you control: it can refuse to start another cycle, regardless of what the model proposes. Anthropic’s Claude Code team describes loops as agents “repeating cycles of work until a stop condition is met” and treats selecting the loop and its stop condition as an engineering problem. Anthropic’s loop-engineering guide

Define the task’s finish line first

A watchdog cannot reliably tell whether an agent is stuck if the task has no observable definition of done. Before the run, record the goal, a verification step, and the stopping rule. For a coding task, verification might mean that a specified test command passes or that a particular file or behavior exists; the exact criterion depends on the task. A 2026 preprint describes a reusable loop specification with a trigger, goal, verification step, stopping rule, and memory. The preprint on engineering coding-agent loops

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Distinguish successful completion from other ways a run can end. Your host should make an explicit decision for each outcome: continue after a tool result, finish when the goal is verified, fail when the task cannot proceed, or hand off for human review when the result is ambiguous. A model response that does not request a tool is not automatically proof that the coding task is complete; apply the task’s verification criterion.

Choose controls that match the failure you want to catch

No single signal identifies every bad loop. A hard budget limits the entire run; a repeated-call detector catches a narrower pattern; and a supported blocking hook can deny a particular tool action. These are complementary controls, not interchangeable guarantees.

Control What it can catch Trade-off Enforcement point
Maximum iterations or elapsed time An overlong run, including loops that vary their calls A slow but productive task can reach the limit The host orchestration loop
Repeated-call detection Runs of equivalent tool calls, such as the same command with the same normalized arguments Legitimate polling or test reruns can look repetitive Tool-call history in the host
Progress monitoring Activity that continues without meaningful outputs, changed files, or verified milestones Requires a task-specific definition of meaningful progress Host-side run and task state
Blocking tool hook A disallowed or suspicious impending action covered by that hook Availability and blocking behavior vary by platform The platform’s hook mechanism

There is no universally established optimal iteration or time limit in the sources here. Set budgets for your own workflow and treat signals as reasons to inspect or intervene, not as proof that every long run is defective.

Build the watchdog at the host boundary

A basic orchestration loop should classify the model’s stop outcome, record each tool call, enforce a finite budget, and check the task’s verification condition. The sequence below is a design checklist, not code or a report of an implementation:

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  1. Start with a task record. Store the goal, verification condition, run budget, and what the host should do when a limit is reached.
  2. Inspect each model response. Continue only for a response that requests tool execution; handle completion, errors, and other stop outcomes separately, following the API’s documented behavior.
  3. Before executing a tool, check the budget and call history. Record the tool identity and normalized arguments so equivalent calls can be compared. Decide how many repetitions are suspicious for this workflow rather than assuming one threshold fits all.
  4. After execution, assess progress. Compare meaningful evidence—such as changed files, useful tool output, or completed verification milestones—not just whether a process is still active.
  5. Enforce the stop rule. When the budget is exhausted or a suspicious pattern is detected, stop before the next cycle or pause for review. Return a useful diagnostic instead of silently continuing.
  6. Record why the watchdog intervened. Log the triggering signal and the relevant call or budget state so a person can distinguish a genuine loop from a long task that was making progress.

Use platform hooks only when they can actually block

A platform hook can add a guard close to a tool action, but it is not a universal agent feature. Anthropic’s Claude Code guidance documents a PreToolUse hook that can inspect an impending call; exiting with code 2 denies that call. This is Claude Code-specific behavior. It does not establish that another coding-agent product has the same hook, event, or denial semantics. Anthropic’s Claude Code steering guide

A hook is useful for a policy tied to a specific tool action. It does not replace a host-level total-run budget unless the platform provides a suitable mechanism and you have confirmed its behavior. If a hook merely reports a warning, describe it as monitoring—not as a control that stops execution.

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Interpret signals without stopping legitimate work

Repeated actions are clues, not verdicts. A test command may need to run again after a code change; a tool may poll for an external process to finish. Conversely, varied tool calls can still fail to move a task toward its goal. Combine call history with the task’s verification criteria and progress evidence.

  • Repeated equivalent calls: compare tool identity and normalized arguments, then consider whether the task reasonably requires repetition.
  • Activity without progress: distinguish a busy process from one producing meaningful results or reaching milestones.
  • Growing resource use without verified movement: treat token growth as one possible warning signal, not a standalone diagnosis.
  • Budget reached: apply the preselected response rather than letting the run continue indefinitely.

A public loop-monitor example discusses repeated actions, stalls, and token growth as possible signals. Its “last 5 tool calls” example is illustrative, not a threshold validated for all agents. The public loop-monitor guide

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Choose a recovery path and make it visible

When the watchdog fires, the host needs an explicit recovery policy. It can terminate the run, pause for a person, or allow a bounded retry with a changed strategy. The sources do not establish one best policy. Whichever you choose, return the reason for intervention and enough context for the next decision; an opaque stop is difficult to distinguish from a broken run.

Do not claim that the watchdog saves time, tokens, or failed runs unless you have measurements from your own logs or reproducible tests. A 2026 preprint on infinite agentic loops reported 68 manually confirmed failures across 47 projects from 74 potential findings, with 91.9% precision for its analysis method. Those are results from the study’s repository analysis and manual review—not an estimate of how often all coding agents loop. The IAL-Scan study

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