6. Tool Calling

Let the model pick and invoke tools. Build at least three: a calculator, a live HTTP call (e.g. Open-Meteo, no key needed), and a text formatter. The model must route correctly and handle a tool error gracefully.

Watch For

Tool output too large to fit in context — truncate before returning
The model picking the wrong tool on ambiguous queries
External providers fail in ways your model can’t “reason” around

Reliability Patterns

Apply these immediately:

Pattern	Purpose
Retries with backoff + jitter	Transient errors (timeouts, 429s, some 5xx)
Fallback chains	Cheaper → stronger, or Provider A → Provider B
Circuit breakers	Prevent a failing provider from cascading into an incident

Resources

OpenAI function calling · Claude tool use