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

Annotations already declare a safe, read-only, idempotent, closed-world call; the description adds real substance on top by explaining that the user does the uploading and style selection on the external site and gets a watermarked preview in minutes. That clarifies what the tool does NOT do (build the mosaic itself), which the annotations cannot express. It stops short of stating whether the link expires or is per-user, a minor remaining gap.

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?

Three sentences, front-loaded with the outcome (the link) before the mechanics and the routing rule. Dense but every clause carries information; the parenthetical photo-count and audience list is slightly long but genuinely helps the agent judge fit.

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?

With no output schema, the description correctly fills that gap by saying the return value is a link and describing what the user will see there. Preconditions, alternatives, and the human-in-the-loop flow are all covered, so an agent can call this correctly without further context.

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 coverage is 100%, so both parameters are already documented, and the description mainly echoes the optional style/occasion semantics. It does add a small amount of meaning, e.g. that occasion is only used to tailor tips and that the site previews styles regardless, but that is largely redundant with the schema text. Baseline 3 is appropriate.

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?

States a concrete action (returns the link where the user builds a photo mosaic) plus a one-line definition of what a mosaic is and its photo-count sweet spot. This is clearly distinct from list_mosaic_styles and the shape-collage siblings, which are named or implied elsewhere in the description.

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?

"Call it only after the user has decided to make a photo mosaic; to show the options first, use list_mosaic_styles" gives an explicit precondition, an explicit exclusion, and the exact alternative to route to. Nothing is left to inference about ordering.

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