Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavior beyond them: the call returns both a credit estimate and a verdict on whether the user's balance covers it, which tells the agent this is a non-charging preview rather than a purchase.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single front-loaded sentence with both the estimate and the balance check, and no filler. Every clause carries information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With 8 parameters, zero required, and no output schema, the description should clarify how to combine inputs per type (e.g. video needs duration and resolution, image needs quality/aspect_ratio) and what the response shape looks like. It covers the response concept but leaves input-combination guidance entirely to the schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so every parameter including enums and the model cross-reference to list_models is already documented. The description adds no additional parameter meaning such as which fields matter for which 'type', so the baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific action (work out credit cost) and the exact subject (a generation, with balance-coverage check). It cleanly separates this from the cost-incurring siblings like generate_image or generate_video and from get_balance, which only reports the balance.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is implied rather than stated: an agent can infer this is a pre-flight dry run before a generation, but the description never says when to call it versus go straight to generate_*, nor whether it's mandatory or optional. No alternatives or exclusions are named.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.