API Calling
An agent reaching out to an external web service to fetch data or make something happen.
Think of it like
Phoning another department to get a record pulled or an order placed — you don’t do it yourself, you ask the right desk.
Example
A travel agent hits an airline’s API to check live seat availability rather than guessing which flights exist.
How it actually works
Most useful agent tools are thin wrappers around APIs: the model picks the call and arguments, your code makes the HTTP request, and the response returns as an observation. The hard parts are unglamorous — auth tokens, rate limits, pagination, and errors the model has to interpret and retry. The model supplies intent; the plumbing supplies reliability.
For product teams
It is how an agent plugs into the systems you already run — CRM, calendar, payments.
For engineers
A tool whose execution issues an authenticated HTTP request to an external service and returns the parsed response to context.
Related
- Tool Use — The general capability this is one flavor of.
- MCP — A standard protocol for exposing tools and data to models.
- Tool Result — What the API sends back into the loop.
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