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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavioral facts beyond that: listing mode returns counts, style facets are 'derived tags', color facets are hue buckets or 'neutral', and stack encodes framework/CMS/host. It does not say how results are ordered or what happens when `limit` truncates a large facet, which is the 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 tight sentences, front-loaded with the primary behavior and ending with the routing rule against search_designs. The only redundancy is re-listing all seven facet names, which the input schema enum already provides.

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 spends words on return shape (values with counts vs. sites having a value), which is the critical missing structure. For a three-parameter read-only tool this is nearly sufficient; only the `limit` semantics and result ordering are left unstated.

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 67% and the description clarifies the trickiest parameter, `value`, by explaining it must come from the facet listing and giving realistic examples ("Inter", "blue", "pill", "next.js"). It also disambiguates facet meanings the enum alone cannot (hue bucket vs neutral, derived tags). The `limit` parameter receives no explanation in either place, keeping this below a 5.

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 states a specific resource (the index) and the two distinct modes of the tool: without `value` it enumerates facet values with counts, with `value` it lists sites carrying that value. Concrete examples (every font family, every style tag) and the facet enumeration make the operation unmistakable and distinct from search_designs.

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?

It gives explicit selection guidance for both modes and an explicit exclusion with a named alternative: 'Not for multi-criteria queries (use search_designs).' An agent can decide between browsing and searching without opening either schema.

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