I Built an AI Agent with Claude's Tool-Use Loop (Web Search, SQL, and More)

"AI agent" gets thrown around so much I figured I should just build one instead of reading more threads about it. The core idea turned out to be small: you put Claude in a loop and hand it some tools. It picks a tool, you run it, you hand back the result, and it keeps going until it has an answer. Code is here if you want to skip ahead: claude-research-agent . What it can do Give it a task and it works out the steps on its own. Mine can: search the web (no API key for this part, it just hits DuckDuckGo's HTML page) open a URL and pull the readable text out do math without me trusting eval run read-only SQL against a SQLite file read local files, but only inside the project folder save findings to a notes file The loop is basically the whole thing Honestly this is most of it: messages = [{ " role " : " user " , " content " : user_message }] for _ in range ( MAX_STEPS ): response = client . messages . create ( model = " claude-sonnet-5 " , max_tokens = 2048 , tools = TOOL_SCHEMAS , messages = messages , ) messages . append ({ " role " : " assistant " , " content " : response . content }) if response . stop_reason != " tool_use " : return final_text ( response ) tool_results = [] for block in response . content : if block . type == " tool_use " : result = run_tool ( block . name , block . input ) tool_results . append ({ " type " : " tool_result " , " tool_use_id " : block . id , " content " : result , }) messages . append ({ " role " : " user " , " content " : tool_results }) The thing to watch is stop_reason . If Claude says tool_use , it wants you to run something. You run it, drop the result back into the conversation as a tool_result , and loop. When it stops asking for tools, you're done. The MAX_STEPS cap is just there so a confused agent can't spin forever. Tools are just functions Each tool is a Python function plus a little JSON schema telling Claude when to reach for it. Want a new capability? Write a function, add its schema. The loop never changes, which w