---
title: "build tool · RUAL Documentation"
description: "Define a tool Claude can call and pick the function that runs it. The function receives the model's arguments as in-pins and returns the result back to…"
canonical: https://docs.rual.nl/block-types/anthropic/anthropicconnection_build_tool
language: en
---

# build tool

This block is part of the [`anthropic`](https://docs.rual.nl/block-types/anthropic) group and was last modified in core [`v15.0.0`](https://docs.rual.nl/core-versions/150000).

### Function Selection Required

This block requires you to choose a custom function to execute when triggered. You must manually select the function you want to use using the function selector modal. To access the modal, click the white button on the block.

Define a tool Claude can call and pick the function that runs it. The function receives the model's arguments as in-pins and returns the result back to Claude. Feed the output into a message block's tools pin.

- name required `value` Tool name (snake_case), e.g. get_weather. Claude uses it to decide when to call the tool.

- description `value` What the tool does and when to use it. The clearer this is, the better Claude calls it.

- parameters `anthropicschema` The shape of the tool's arguments. Build it with the 'build output template' block. Omit for a no-argument tool.

- tool `anthropictool` The tool definition; wire into a message block's tools pin.

| `tool` |
| --- |
| `skill` |
| `function call` |
| `claude tool` |
| `agent tool` |
| `define tool` |

A typical wiring for [build tool](https://docs.rual.nl/block-types/anthropic/anthropicconnection_build_tool): [value](https://docs.rual.nl/block-types/value/value_default) feeds the `name` pin; the `tool` out pin feeds [send message](https://docs.rual.nl/block-types/anthropic/anthropicconnection_message).

![Studio canvas example for the build tool block: typical wiring for build tool.](https://docs.rual.nl/canvas-examples/anthropicconnection_build_tool.png)

### Version history

Introduced in [`v15.0.0`](https://docs.rual.nl/core-versions/150000).