Tool description
The text an MCP server publishes about each of its tools, which the model reads to decide what to call and how.
Every tool a server offers comes with a name, a description and a schema for its arguments. The client passes all three to the model, and the model uses the description to decide when the tool is the right one and what to put in each argument.
The person using the agent usually never sees it. Most clients show a tool's name and not its description, so a sentence in there is read by the model and by nobody else.
It is the part of a server that talks to the model directly, which is why this site reads it for instructions that do not belong there.
Assuming a description is documentation for people. It is input to a model, delivered inside the trusted part of the context, and the model treats it as instructions.
Related terms
See Tool description on a real listing
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