What Does stop_reason Tool_Use Mean in Claude API?
Spot Claude’s tool call intent by checking stop_reason=”tool_use” in API responses—vital for conversation handling beyond text or length checks.
Question
How can you tell if Claude wants to make another tool call in a conversation?
A. Check if the response contains the word “tool”
B. Check if the response is longer than usual
C. Look at the stop_reason field for “tool_use”
D. Count the number of message blocks
Answer
C. Look at the stop_reason field for “tool_use”
Explanation
In the Claude API Messages response, the stop_reason field indicates why generation halted: “tool_use” specifically signals Claude intends another tool call, typically with a tool_use content block containing the tool name and arguments for execution. Check this programmatically post-API call—presence of stop_reason: “tool_use” triggers handling the embedded tool request, unlike scanning text for keywords (A, unreliable), length heuristics (B, coincidental), or block counts (D, ambiguous). This structured metadata ensures seamless tool-using conversation flow without guesswork.