Tool Use
Also: function calling, tool calling
Tool use lets Claude call external functions and APIs during a conversation. You define the tools Claude has access to — search, database lookup, sending an email, running a calculation — and Claude decides when to call them, what inputs to send, and how to use the results in its response. It's the mechanism that turns Claude from a text generator into something that can take actions and interact with real systems.
In practice
You give Claude access to a search function and a calculator. It's answering a question and realizes it needs current data — it calls the search tool, gets results, incorporates them, then uses the calculator to run a number. Tool use is Claude's ability to reach outside the conversation and take real actions, not just generate text.
Related concepts
Where Tool Use shows up
10 articlesTool use is the mechanism that lets Claude take actions — call APIs, run code, search files — instead of just generating text. Here's exactly what happens when Claude uses a tool.
Vague instructions get vague results. The difference between "find me that doc in Notion" and an instruction that actually works — every time.
Defining tools, parsing responses, handling multi-turn tool calls, parallel tool use, and the failure modes that will bite you in production.
Some agencies are not just using Claude internally — they are building Claude into the work itself. What that looks like, what clients actually want, and how to avoid the obvious failure modes.
Claude can't open your spreadsheets directly — but it can write the formulas, clean your data, explain your numbers, and build a spreadsheet from scratch. Here's what works and what doesn't.
Anthropic's ant CLI gives you direct access to every Claude API endpoint from the command line — messages, models, batch jobs, agents. Install it, set your API key, and run API calls without writing application code.
Anthropic's Word add-in puts Claude in a sidebar that reads your whole document, suggests edits as tracked changes you accept or reject, and works without leaving Word. Requires a Team or Enterprise plan.
Every company has ten things they could automate with AI. About two of them are actually good starting points. Here's the framework for finding them.
Tool use is the mechanism that turns Claude from a text generator into something that can actually do things — search the web, run code, query your database, send messages.
Data teams have a counterintuitive relationship with Claude — it is not about the analysis, it is about everything around it.