I want AI to do something in our app, not just produce text

Function calling (also tool use) is how a model says 'call function X with parameters Y' in structured form rather than free text. You execute the function, return the result, and the model continues. That is the foundation for agents placing orders, checking calendars or sending invoices.

Try this first

1. 1First decide which actions are safe for AI: read-only against internal systems is low risk, writes or moving money is high risk and needs at least human confirmation.
2. 2Describe each function as JSON schema: name, description, parameters, types. The clearer the description, the fewer wrong or stray calls the model makes.
3. 3Implement a 'tools' layer in your backend: one place where every call passes validation (is this user allowed, are parameters sound), not the AI output going straight to your production API.
4. 4Logging: store every tool call with input, output, user and model version. On a wrong call you want to trace exactly what the model asked.
5. 5Start small: one function like 'find customer by name', then 'create draft invoice'. Only when that is stable, add 'send invoice' behind a confirmation step.

None of the above fits?

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