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

Annotations indicate a mutating operation (readOnlyHint false) that is idempotent (idempotentHint true). The description adds a small amount of behavioral scoping by specifying 'text watermark' and 'one PDF', but it does not disclose whether the original file is preserved, what the output format is, or the temporary URL requirement (the latter is in the schema). No contradiction exists between description and annotations.

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 8-word sentence with no filler or redundancy. It is front-loaded with the action and object. While a bit more guidance would be useful, the structure is appropriately minimal for a clear purpose.

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?

Given the moderate complexity (8 parameters, 3 required) and the presence of an output schema, the description is minimally adequate. It mentions the single-PDF scope but does not explain the operational flow (download, watermark, return) or usage relative to sibling tools. This leaves gaps that an agent might need to fill by inspecting the schema or output schema.

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?

All 8 parameters are documented in the schema with 100% coverage, so the description does not need to explain them. The description contains no parameter-specific details, but it also does not conflict with schema descriptions. Baseline 3 is appropriate because the schema carries the burden.

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 ('Add') and a specific resource ('text watermark to one PDF'), making the tool's function unambiguous. It clearly differentiates from siblings like merge_pdfs and split_pdf by focusing solely on watermarking. There is no ambiguity about what action is performed.

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 provides no information about when to choose this tool over alternatives such as merge_pdfs, split_pdf, or conversion tools. It neither states typical use cases nor excludes scenarios where another tool would be more appropriate. An agent is left to infer usage solely from the tool name and sibling list.

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