Using another app or service
A tool lets an AI app use other software, such as a calendar app, weather service, or company database. A tool can also perform a task within the AI app. The model names the tool and supplies the details it needs; the app makes the actual call.
Suppose you ask an AI assistant to arrange a meeting. The model requests a tool to check free times in your connected calendar app. The AI app checks that it has permission to view your calendar, contacts the calendar service, and gives the available times back to the model. Creating the event would be another tool call and may need your approval.
MCP is one way AI apps connect to tools offered by other software.
Checks before taking action
The app must check what each tool can access and whether a requested action is allowed, especially before changing data or sending a message.
It must also handle errors, repeated calls, and misleading text from other services, including prompt injection. A correctly formatted tool call can still ask for the wrong action.