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

With no annotations supplied, the description carries the full burden and does meaningful work: it discloses a per-image price of €0.001, that billing hits the API key in the Authorization header, and the default position and opacity. It does not clarify whether url is mandatory or whether text/logo_url are mutually exclusive, and says nothing about failure modes, so it is strong but not complete.

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?

Front-loads the capability and output formats, then a single compact 'Parameters —' run gives each field in name: meaning form. It is dense rather than padded, though the trailing parameter clause reads as one long run-on that could be broken for faster scanning.

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?

An output schema exists, so return values need no explanation, and the description fully covers inputs, cost, and auth. The remaining gap is input composition: all six params are optional in the schema and the description never states that url plus at least one of text/logo_url is required, which an agent needs to call it 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?

Schema description coverage is 0% and every property is an undescribed nullable string, so the description is the only source of meaning. It documents all six parameters, and crucially supplies enumerations the schema lacks entirely: position values with default bottom-right, opacity range 5–100 with default 35, and format jpeg|png|webp.

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?

Opens with a specific verb+resource ('Text or logo watermark') and enumerates the modalities (corner, center, tiled, opacity) plus output formats. No sibling in the list does watermarking, and the definition makes that scope unmistakable without needing to open the 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?

Provides concrete operative context (cost per image, required Bearer auth, supported formats) so an agent knows the conditions of calling it. It stops short of explicit when-to-use/when-not guidance or naming alternatives such as compress or remove_background, so it does not reach 5.

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