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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds only 'Returns the result file', which implies a new output file rather than in-place mutation — useful but thin; it says nothing about processing time, page limits beyond the schema's 50 MB, or whether the source file is preserved.

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 short sentences, front-loaded with the action, with zero filler. The customization note follows immediately and the return behavior closes it out.

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 simple file-transform tool with fully documented parameters and no output schema, the description covers the essentials: accepted input type and that a result file is returned. Only the fate of the input file and any output naming convention are left unstated.

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 the baseline is 3. The description echoes three of the five option fields (position, format, start) but omits 'from' and 'size', adding no semantics the schema does not already carry.

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 ('Number the pages of a PDF') plus the customizable dimensions, which is far more concrete than the title alone. No sibling does page numbering, so there is little risk of confusion, but the description never explicitly contrasts itself with related tools like watermark-pdf or text-to-pdf.

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?

'position, format and start number are up to you' hints at configurability but gives no when-to-use / when-not-to-use guidance and names no alternative. An agent gets no help deciding between this and, say, watermark-pdf for stamping content onto pages.

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