What this means in practice
Charges come from billable work performed by a step, such as a model turn, web capture, or conversion.
Reading local files is not billed as a tool operation.
Check run details to see which work consumed credits.
Practical guidance
The number of tools available is not itself a usage charge. Credits are tied to work that a run performs, so the useful question is which step used a billable capability. A model turn, web capture, or file conversion can consume credits; reading a local file is not charged as a tool operation. A workflow that uses more steps can therefore have a different total from a short interaction, even though the tools are included.
To understand a run, open its step details and identify the operations that actually executed. Compare that trace with the result you asked for: unnecessary model turns or repeated conversions are places where a request or workflow can be made more focused. This gives you a practical way to manage usage without disabling tools you need.