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

Annotations already indicate readOnlyHint=false and destructiveHint=false, so the description does not need to restate that. It adds meaningful context beyond the annotations: it specifies that the operation preserves order, that it returns a file_id for chaining, and that the download URL expires in ~1 hour. These details help the agent anticipate side effects and output format, which is valuable for a mutating tool.

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 a single sentence that is dense but free of filler. It front-loads the core action, then states the output and the expiry time. Every word earns its place, and it is immediately scannable by an agent.

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?

The tool is simple with only two parameters and no output schema. The description explains what it does, the order preservation, and the return format (file_id and download URL). It does not mention edge cases like invalid page numbers or the behavior when pages are out of range, but for a basic selection tool this is not critical. Given the low complexity and high schema coverage, the description is sufficiently complete for an agent to invoke the tool correctly.

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 100% (both 'pdf' and 'pages' have descriptions in the input schema). The description adds no new semantic information about the parameters; it repeats the example '1,3,5' which is already in the schema. Since the schema fully documents the parameters, the description contributes little beyond what is already structured. 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 states a specific verb ('Keep only the specified pages') and resource ('a PDF'), with an explicit example ('[1,3,5]') and the effect ('drop the rest, preserving order'). It clearly differentiates the tool's function from siblings like split_pdf or merge_pdfs by specifying that it outputs a single PDF with selected pages rather than splitting or merging.

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 usage: use this when you need to extract a subset of pages from a PDF while preserving order. However, it does not explicitly mention when NOT to use it or name any alternative tools (e.g., 'for splitting into multiple PDFs, use split_pdf'). It provides no exclusionary guidance, so the agent must infer usage from the action described.

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