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

Annotations already declare it is a non-destructive, non-idempotent mutation and that an output schema exists, so the safety profile is covered. The description usefully adds that the watermark hits every page and that both operations can run in one call, but does not warn that repeated invocations stack stamps (consistent with idempotentHint=false) or what the output artifact is.

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 with no padding; the combinability statement is front-loaded and the format-string caveat immediately follows where it is needed.

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?

With an output schema and annotations present, the description only needs to convey the operational model, and it does state the two modes and their combination. The remaining gap is sparse guidance on file-source selection and failure modes when neither operation is requested.

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 67%, and the description adds genuinely non-schema detail for the page-number format string ('%d' used twice, with an example). However, it says nothing about the four mutually exclusive file-source parameters or the watermark styling options (color, opacity, rotation, size), which remain undocumented on the description side.

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 gives a specific verb+resource (number pages, stamp a text watermark on every page) and clarifies the operations can be combined. It is clearly distinguishable from any sibling (no other tool stamps or numbers pages), though it does not explicitly name a sibling it is not.

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?

There is no guidance on when to use this versus alternatives, no preconditions (e.g., which of file/file_id/file_url/library_file_id to supply), and no note that at least one of page_numbers or watermark should be provided since nothing is required.

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