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 those. It adds useful behavioral context: that the watermark is diagonal grey, that it returns a file_id for chaining, and that the download URL expires in ~1h. This goes beyond the annotations and gives the agent practical information about the result and its lifecycle.

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 two sentences with no fluff. It front-loads the action and key examples, then states the output format. Every word adds value, making it efficient and easily scannable.

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 two-parameter tool with no output schema, the description covers the essential aspects: what it does, the output, and the time-limited URL. It does not mention error conditions or file size limits, but these are not critical for a watermark operation. The description is sufficiently complete for an agent to call 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?

The input schema already fully describes both parameters (pdf as file_id or base64, text as watermark text) with 100% coverage. The description only adds examples of text (DRAFT, CONFIDENTIAL) which are illustrative but not necessary. It does not clarify any additional semantics beyond the schema, so it meets the baseline of 3.

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 uses a specific verb 'Stamp' with a clear resource 'PDF' and describes the action in detail ('diagonal grey text watermark across every page'). It also names the return value (file_id and download URL), which distinguishes it from any sibling tool. No other sibling performs watermarking, so it is clearly unique.

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 clearly states the purpose and output, implying when to use it (when you need to watermark a PDF). However, it does not explicitly mention alternatives or when not to use it, such as comparing to number_pdf or set_pdf_metadata. The context is clear enough for an agent to infer usage, but it lacks explicit exclusions or comparisons.

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