Watermark an image

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

With no annotations, the description carries the burden of explaining behavior. It does disclose the core effect (adding a watermark), supported features, and the 'text' vs 'watermark_path' constraint. However, it does not explain what happens if both are supplied, how the source image is selected, or the output behavior, leaving the agent to infer important runtime semantics.

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 tight sentences with no filler. It front-loads the action, summarizes key options, and closes with the most important invocation constraint. Every sentence earns its place.

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?

The description is sufficient for basic selection and gives the key either/or constraint, and the rich schema plus output schema reduce the need to restate parameters. However, with zero required parameters and no mention that the base image must be supplied via url, path, or base64_data, an agent could easily construct an invalid call. For a 23-parameter tool, that is a meaningful completeness gap.

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 description coverage is 100%, so the schema already documents all 23 parameters. The description adds some value by highlighting the text/watermark_path mutual exclusivity and grouping position, opacity, rotation, and tiling, but it does not meaningfully enrich the schema's parameter details.

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 a specific operation ('Add a text or image watermark') on a specific resource (an image), so an agent can tell this is the watermarking tool. It does not explicitly compare against sibling tools, but the verb and object are unambiguous enough to prevent confusion with resize, crop, rotate, or convert.

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 intended use case is implied: use this when you need to add a text or image watermark. However, there is no explicit when-not-to-use guidance or mention of alternatives among the 13 sibling tools, so the agent must infer selection from the title and first sentence.

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