A team is implementing tool use (function calling) with Claude to enable a database query tool. Claude returns a tool_use content block. What must the implementation include to correctly complete the agentic loop?
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Short Explanation
Here's the deal — you need to send a new messages request that keeps the assistant's tool_use block and adds a user message with the tool_result. That lets Claude see the call and the output before it continues.
Full Explanation
The correct agentic loop for tool use requires sending a new messages request that includes the original conversation history, the assistant's response containing the tool_use content block exactly as returned by the API, and a new user message with a tool_result content block containing the tool_use_id and the tool's output. This multi-turn structure allows Claude to see both its tool call and the result before generating its final response. Sending the tool result with role assistant alongside Claude's previous response is wrong because tool results are sent as user role messages, not assistant. Sending the tool result directly to a separate /v1/tools/result endpoint is incorrect because there is no separate tool result endpoint; all interaction goes through the Messages API. Including the tool result in the system prompt of the next API call loses the structured tool use/result relationship that Claude's training expects and produces unreliable behavior.