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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered structurally. The description still adds genuinely new context: that the call consumes nothing ('without generating') and that pricing is also surfaced at the confirmation prompt, which prevents redundant calls. No contradiction with the annotations.

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?

Three short sentences, each earning its place: what it does, when to call it, and when not to. The key distinction ('without generating') is front-loaded in the first clause.

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 zero required parameters, full schema coverage and a no-op safety profile, the only remaining ambiguity is the shape of the return value (a bare credit figure versus a breakdown), which is not addressed and there is no output schema to cover it. For a simple read-only estimator this is a minor gap rather than a blocking one.

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 count, model and resolution are already documented, including the default behaviours and the resolution/cost relationship. The description adds nothing parameter-level beyond the general notion of cost, so the baseline 3 applies.

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 states a specific verb and resource: it reports the credit price of an image generation without performing one. It is distinguishable from generate_image (which actually spends credits) and from the sibling estimators by tool name and title, though the body text says only 'generating' rather than 'image generation', so the resource specificity leans on the title.

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?

It gives both the trigger ('when the user asks what something would cost') and an explicit exclusion ('You do not need it before generating: the confirmation prompt already states the price'), which pre-empts a very likely wrong invocation. This is exactly the when/when-not guidance the dimension rewards.

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