What is Function calling?
Verified 5 August 2026
The model is given function schemas and returns a structured call the application executes. Schema-constrained output is what makes tool use reliable enough to build on.
A tight schema is a feature rather than a limitation — the fewer degrees of freedom the model has, the fewer ways the call can be wrong.
Common questions
What is Function calling?
Function calling is a model’s ability to emit structured arguments for a named function rather than free text, enabling reliable tool invocation.
How does Function calling work in practice?
A tight schema is a feature rather than a limitation — the fewer degrees of freedom the model has, the fewer ways the call can be wrong.
See it working
The free tier is 10,000 requests a month with no card — enough to test any of this against your own queries.