What is function calling?
Function calling is the capability that lets an AI model request one of your existing software actions, with the right inputs filled in, so it can fetch real data or get something done.
The simple explanation.
Every business has a set of things staff are allowed to do: check stock, issue a credit note, book a slot. Function calling is how you hand that same list to an AI model. Each action is described in plain terms along with the information it needs. When a request comes in, the model picks the right action and fills in the blanks. It does not write software. It decides which piece of your existing software should run, and with what inputs.
Function calling versus a tool call.
The two terms get used interchangeably, and the difference is small but useful. Function calling is the capability: your agent has been given a defined list of actions it may request. A tool call is one single use of that capability, such as looking up invoice INV-2291 on a Tuesday afternoon. The capability is what you design once during a build. Tool calls are what happen thousands of times afterwards in production, and what you read back when you want to know how the agent behaved.
Where it shows up in daily operations.
A customer messages on WhatsApp asking whether a delivery went out. Without function calling, the agent can only offer a general reply. With it, the agent requests the delivery lookup, receives the real status, and answers with the tracking number. The same applies to creating a quotation, updating a lead stage, or reserving stock. Function calling is what turns your CRM, inventory and messaging tools into things an agent can operate, rather than things only your staff can operate.
The Voltade take
When we scope a custom agent, most of the work is deciding which functions it should have and what each one is allowed to touch. A sales agent might read the pipeline and create a lead but never issue a refund. Defining that list carefully up front is what keeps an agent both useful and safe once it is live in Envoy CRM.
More from the glossary
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