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

The description discloses several behavioral traits beyond the annotations: 'Costs 1 credit per call,' 'Returns a temporary download link (valid 15 minutes),' and instructs the agent to 'Always include that link in your reply.' It also clarifies the overlay behavior (every page or specified pages) and the text/image constraint. This enriches the agent's understanding of side effects and required follow-up actions, and does not contradict any annotation.

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 four sentences, front-loaded with the purpose, then usage scope, cost, and return-link instruction. Every sentence adds distinct value: purpose, operation details, cost, and output handling. No fluff or repetition; it is compact and well-ordered.

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 tool with 10 parameters but a fully described schema and no output schema, the description covers the essential operational aspects: what it does, the cost, the temporary link, and the instruction to include it in replies. It also notes the page-scoping option. Given the schema already documents all parameters, the description is sufficient for an agent to invoke the tool correctly and handle the result appropriately.

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 provides detailed descriptions for all 10 parameters (100% coverage), so the baseline is 3. The description adds little beyond that: it repeats the max 200 characters and the 'OR' constraint, and mentions 'Image watermarks need the JSON body,' which is already implied by the schema's image property. It does not clarify nuances like the interaction between color and font_size (text-only) beyond what the schema states, so it does not significantly elevate parameter understanding.

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 clearly states the tool's function: 'Add a text or image watermark to a PDF.' It specifies the resource (PDF), the action (watermark), and the two modes (text or image). This is unique among sibling tools, which are all distinct PDF operations like merge, split, rotate, etc., so there is no ambiguity.

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 gives clear context on what the tool does ('overlays text or image on every page or on pages'), and notes a key requirement ('Image watermarks need the JSON body'). However, it does not explicitly compare to alternatives or state when not to use it. Since the tool's purpose is self-evident and distinct from siblings, the guidance is adequate but lacks explicit exclusions.

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