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

Beyond the annotations (readOnlyHint=true, idempotentHint=true, destructiveHint=false), the description discloses that a NEW PDF is returned rather than the original modified, that each stamp is re-verified in the output file before the link is issued, and that the watermark is removable with editing software. Those are meaningful behavioral facts the annotations cannot convey. It is slightly short of a 5 only because it says nothing about processing time or failure modes when a page range is out of bounds.

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?

It is front-loaded with the usage trigger, and every sentence carries information: use case, inputs, return behavior, verification, limitations, and sibling exclusion. It is a dense single block rather than a structured list, which makes the embedded constraints (opacity/angle ranges) slightly harder to scan, but there is no filler.

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 present, the description need not explain return structure, yet it still summarizes the result ('a new PDF with the text centered on each chosen page'). Combined with rich annotations, this covers nearly everything an agent needs to call the tool correctly; the only gap is the contradictory character limit for the text parameter.

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%, so the baseline is 3, and the description does add real meaning by stating the text is centered on each chosen page and by giving the page-range syntax ('1-3, 8'). However it introduces a factual error: it says the watermark text is 'up to 40 characters' while the schema's maxLength is 80, which could cause an agent to truncate valid input unnecessarily.

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 opens with a specific verb+resource ('add a watermark to a PDF') and enumerates concrete stamp use cases (DRAFT, CONFIDENTIAL, COPY, SAMPLE) plus partial-page marking. It explicitly distinguishes itself from the sibling tools by ending with 'Do not use for page numbers,' so an agent can route between stamp_watermark and stamp_page_numbers without opening either schema.

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?

It states when to use ('Use this when the user wants to add a watermark'), when not to use ('Do not use for page numbers', no image/logo watermarks, no password-protected PDFs), and names the sibling alternative implicitly. Both the positive trigger and the exclusions are explicit rather than inferred.

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