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

Beyond the annotations, the description adds meaningful behavioral context: 'Deterministic' guarantees reproducible output and aligns with idempotentHint, and '$0.003' discloses cost, which is important for an agent deciding whether to invoke it. It does not describe side effects like fetching URLs, but the simple merge semantics make this a minor gap.

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?

The description is extremely concise: one front-loaded sentence communicates the core operation, constraints, and ordering, followed by two short high-value facts (determinism and price). There is no filler or repetition of schema details.

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 low-complexity tool with two parameters and no nested objects, the description covers the operation, constraints, and cost, while the schema handles payment parameter semantics. The only notable absence is the explicit return format (e.g., the merged PDF binary), but this is reasonably implied by 'Merge 2-10 PDFs into 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?

The schema provides 100% coverage of both parameters, including the detailed x_payment behavior. The description reinforces the 'in order' semantics and 2-10 range already present in the schema but adds no new parameter-level meaning beyond that, so the baseline of 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 is explicit and specific: 'Merge 2-10 PDFs into one, in order' names the verb, the resource, the count constraint, and the ordering guarantee. This clearly distinguishes it from sibling tools like pdf_info and pdf_pages, which inspect or process individual PDFs rather than combining them.

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?

The description implies its usage context—combining multiple PDFs into a single document—but it does not explicitly state when to prefer this tool over alternatives, nor does it mention exclusions or prerequisites such as URL accessibility or payment requirements. The usage is inferred from the operation itself rather than explicitly guided.

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