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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), and the description adds genuinely new behavioral facts: a per-call cost of 5 credits, accepted file input encodings, and the 10 MB size ceiling. It also discloses that output is signed and independently verifiable via verify_url, which is a meaningful trust property not present in annotations. Missing is whether failed/invalid file checks are still billed.

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?

Front-loaded with the action and cost before any field detail, and the terse output-shape notation packs a lot of information into a few lines. The output listing is long but justified by the absence of an output schema, so little of it is waste.

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?

For a four-parameter validation tool with no output schema, the description supplies the return shape, verdict vocabulary, and verification URL — the pieces an agent most needs to plan around the result. Gaps remain around error/failure responses and the meaning and defaults of the paper option.

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?

With 75% schema coverage, the schema already carries baseline documentation, and the description usefully generalizes the accepted input forms (base64, data: URI, or {"url": ...}) to both interior and cover plus the 10 MB cap. However, the paper parameter and its enum (white/cream/groundwood/color stocks) get no explanation at all, and trim is only implicitly covered, so it does not fully close the remaining gap.

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 verb and resource: check a KDP paperback interior and cover PDF against Amazon's published file specs, returning a signed report. An agent can distinguish this from kdp_spine_calc or kdp_puzzle_book without opening the schema. It stops short of a 5 because it never names the adjacent siblings (kdp_report in particular) to make the boundary explicit.

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 — you run a preflight check on manuscript files before upload, and the '5 credits per call' note is decision-relevant cost context. There is no explicit when-not guidance, no mention of prerequisites (e.g., whether a cover can be checked without a spine width), and no routing to alternatives such as kdp_spine_calc or pdf_info.

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