Glossary
Tool call
A structured request from a language model to run a named function (a tool) with specific arguments, such as sending an email or querying a database.
Checks run on our GPUs in Switzerland. Request payloads are not stored.Security
What Tool call means
A tool call (also called a function call) is how a language model acts on the world. Instead of answering in prose, the model emits a structured request: the name of a tool and a set of arguments, for example a tool named send_email with a recipient, subject and body. The application, not the model, executes it and usually feeds the result back to the model.
Tool calls are where an agent’s risk concentrates. The model chooses the tool and fills in the arguments, and both can be wrong: the tool may be more powerful than the task needs, the arguments may be invented (see hallucinated arguments), or the call may have been prompted by instructions hidden in an earlier tool result (see indirect prompt injection).
MCP Guard accepts a tool call either as a string such as db.drop_table(users) or as an object with tool and args, and checks it before it runs.
Related terms
How Tool call connects to the rest of the vocabulary.