Tool
A single action, such as running a task or a function, that an agent can call.
Where a tool lives depends on where it can be reached, not who built it. A centrally hosted tool that others can use is part of the stack. A local tool scoped to one person's harness, like an advanced developer's local MCP server, is part of that harness. An agent's permission to use a tool is always harness. Building a central tool is a stack contribution; wiring your agent to it is harness configuration. Today tools are mostly central and shared; local, harness-only tools are the exception. Watch: personal agents may start creating tools on the fly for one person or task, which would shift part of the tool layer into the harness.
Also called
- Tool use
- Tool calling
- Function calling
Kinds
- Computer use A tool that lets an agent work a computer screen the same way a person would (view, click, type).
- Code execution A tool that runs code the model has written, usually in a sandbox.
Often confused with
- Agent skill A package of instructions and files, written in an open text-based format, that an agent loads only when a task needs it.
Related
- Model Context Protocol An open standard, started by Anthropic in 2024 and now run under the Linux Foundation, for connecting AI systems and agents to outside tools and data in one common way.
How it connects
- Tool is called by an Agent
- Tool is governed by Agent gateway
- Tool comes packaged in a Connector
- MCP server offers Tool