Why we record tool calls, not just model calls
Half of the bugs we see in agents are in the tools around the model. Tracing only the model hides them.
T
Tomás Reyes
8 min
A model call has a clean contract: text in, text out. A tool call is a network request, a database query or a side effect, and it is where most production failures live.
What a tool span stores
The arguments the model chose
The raw response, redacted by your rules
Retries and timing, drawn to scale
The payoff
When a run goes wrong you can see whether the model picked the wrong tool or the right tool failed. Those need different fixes.
