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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds genuinely new behavioral context: nothing is charged and the call counts against the daily read quota — a cost/rate constraint the agent cannot get from 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?

Two tight sentences with the useful constraint (no charge, quota impact) front-loaded. Slightly fragmentary but every element earns its place and there is no filler.

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?

There is no output schema, so the description carries the return burden and does so by naming the two returned items (price in US cents, full license terms). Combined with the quota and no-charge notes, an agent has enough to call this correctly, though enum semantics remain unaddressed.

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 coverage is 50%: photo_id is documented in the schema ('From num_search_photos') but the 'use' enum is not explained anywhere. The description adds no meaning about the enum values (social/web/ad/ai_training) or how they affect price, so it lands at the baseline for partial coverage.

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?

States a specific resource (price and license terms for one use of one photo) with a clear scope of 'one use'. It implicitly distinguishes itself from the licensing sibling via 'Nothing is charged', but never names num_license_photo outright, leaving differentiation to inference.

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?

'Nothing is charged' implies this is a pre-purchase quote rather than a license action, which is useful routing information. However, it never explicitly states when to use this versus num_license_photo, nor mentions prerequisites beyond a note about quota.

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