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A production Claude tool loop should stop when Claude has completed its answer, a tool has failed terminally, a configured run budget is exhausted, the next action is unauthorized, or the response is incomplete and cannot safely continue. Continue only for a valid tool request or a deliberately managed pause. These five conditions are an engineering synthesis of Anthropic’s documented control-flow signals—not an official Anthropic framework.
What tells an application to continue or stop?
Inspect the response’s stop reason before deciding what to do next. Anthropic documents distinctions including end_turn, tool_use, max_tokens, pause_turn, and refusal. These signals describe different control-flow outcomes; they are not interchangeable. Check the supported values for the model and API version you deploy.
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| Signal or condition | Meaning for the loop | Next action |
|---|---|---|
end_turn |
Claude has finished its turn. | Stop and return the response. |
tool_use |
Claude is handing off a requested operation. | Validate and, if permitted, execute the tool; return its correlated result. |
max_tokens |
The response reached the output-token limit and may be incomplete. | Do not present it as a complete answer. Handle under a deliberate recovery policy. |
pause_turn |
A server-tool workflow has paused. | Use the documented continuation flow only if policy and budget still allow it. |
| Refusal | The response indicates a refusal. | Do not execute a tool based on that response; handle it as a refusal. |
Anthropic’s stop-reason guidance describes these distinctions. A tool request is a handoff, not evidence that the user’s task is complete.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errors1. Stop when Claude has finished
When the response ends with end_turn, treat it as a completed turn and return the answer rather than calling tools again. By contrast, tool_use requests an operation. After handling that operation, send its result in the expected format and inspect the next response; do not assume the tool result itself finishes the interaction.
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2. Stop when a tool failure is terminal
Match every tool result to the request that caused it. For client tools, Anthropic specifies that the result follows the assistant’s tool-use message, uses the tool_result type, and carries the corresponding tool_use_id. Mark failed operations with is_error where applicable so an error cannot be mistaken for successful output. See Anthropic’s tool-use implementation guidance.
Classify failures in your application. A transient network problem may be retryable; invalid input, denied permission, or a persistent service error may not be. Anthropic’s tool-use documentation explains error signaling, but does not prescribe a universal retry policy or retry count. Set limits appropriate to the operation, and stop once a failure is terminal or the retry allowance is exhausted.
3. Stop when the run budget is exhausted
An unattended loop needs an explicit bound. Set a maximum number of model/tool turns and, when relevant, time, token, or monetary limits. Choose these limits for the task’s risk, latency, and cost requirements: Anthropic’s cited documentation does not supply a universal budget value.
Claude Code CLI
Claude Code’s CLI reference documents --max-turns for limiting agentic turns in print mode; it exits with an error when the limit is reached. The reference does not list a default limit. This is a Claude Code CLI control, not an automatic bound on a Messages API integration. See the Claude Code CLI reference.
Messages API integrations
Implement the equivalent ceiling in your own loop. Count turns consistently, stop before starting work that would exceed the configured budget, and report that the run ended at its limit rather than presenting partial work as a completed result.
4. Stop before an unauthorized action
Model intent does not grant permission. Check authorization in the application before executing a consequential tool operation, including writes, external messages, purchases, or destructive changes. If approval is required but unavailable, do not silently proceed: deny or defer the operation and return control to an authorized user or system.
Claude Code documents permission modes and unattended behavior, including cases where prompts may be denied when nobody is available to answer. Treat those as product-specific controls; an API integration still needs its own enforcement. See the Claude Code permission documentation.
5. Stop or recover when output is incomplete
Token-limited output
max_tokens means the response may have been truncated. Do not mark it successful merely because text was returned. Depending on the task, you might request a continuation, retry with a revised output strategy, or surface an incomplete result—but only within the same authorization and budget checks.
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Managed pauses
pause_turn can occur in server-tool flows. Continue only through the documented flow for that API behavior, and only while the run remains within policy and budget. A pause is neither ordinary completion nor permission to continue indefinitely.
Oversized MCP tool output in Claude Code
Claude Code’s MCP documentation describes a warning above 10,000 tokens and a default maximum of 25,000 tokens for applicable tool output. It also says oversized successful text results can be moved to a file, while long error results are truncated to retained leading and trailing text. These figures describe Claude Code’s documented MCP handling; they are not universal limits for Claude API clients. Check the current Claude Code MCP documentation for behavior applicable to your version.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A practical control-flow checklist
- Inspect the response’s stop reason before taking another action.
- If it is
end_turn, return the answer. If it is a refusal, handle the refusal without executing a tool. - If it is
tool_use, validate the tool name and input against application policy and authorization. - Execute only approved operations. Return each client-tool result as a
tool_resultcorrelated with its originatingtool_use_id, and mark failures withis_errorwhere applicable. - Classify the result. Retry only failures your application considers transient, with a bounded retry policy; stop on terminal failure.
- Before another turn or tool call, enforce turn, time, token, and cost limits relevant to the run.
- If the response is truncated or paused, use an explicit recovery or continuation path; otherwise report that the work is incomplete.
- Record the stop reason and outcome so operators can distinguish completion, failure, denial, exhaustion, and incomplete output.
Choosing between automatic continuation and returning control
Automatic continuation can reduce interruptions for low-risk, recoverable work, but it adds latency and cost and can compound a bad assumption. Returning control is safer when an action needs approval, a failure is terminal, the output is incomplete, or the run reaches its ceiling. The right boundary depends on the consequences of the tool and the service objective; there is no single retry count or risk threshold established by the cited documentation.
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