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

Annotations already establish read-only/idempotent safety, and the description adds substantial context beyond them: counts cover only book illustrations (museum-artwork collection excluded), only tags on 3+ images are listed, refresh cadence is weekly, and no returned URL is a browse page. This is exactly the kind of operational detail annotations cannot carry.

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 purpose, then usage, then caveats in a logical sequence. Dense but almost every clause carries decision-relevant information; the closing URL warning is slightly tangential but still operationally useful.

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?

Covers call patterns, match semantics, coverage limits, staleness, and the failure fallback. With no output schema, the note that results contain counts and non-browse URLs adequately frames the return shape.

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 baseline is 3, but the description still adds meaning: it explains the semantic effect of omitting facet (top values of all four) and gives a concrete contains example ('ouro' -> 'ouroboros'). It does not restate the limit semantics, which the schema fully covers.

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 exactly what is listed (legal values of the type/subject/figure/symbol filters of search_images) and why (exact-match tags with huge vocabularies). An agent can immediately distinguish it from sibling search_images, which it explicitly references.

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?

Explicit when-to-use ('Look it up here first'), how to call it in each mode (no facet = top values; facet + contains = spelling lookup), and a named fallback ('use it as free text in search_images' query instead') for the no-match case.

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