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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds the useful trait that it 'honors the same filters as search,' but says nothing about result shape, pagination, or how facet counts are bounded. With annotations carrying the safety burden, this is adequate but not rich.

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?

Two front-loaded sentences with no filler: the aggregation behavior comes first, then the pairing guidance. Efficient and readable, though slightly generic in the second sentence.

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 needn't be described, and the schema fully documents the ten filters. The description supplies the one thing the schema can't convey—that it is an aggregation companion to search. Nearly complete for this tool type.

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 ten parameters including the required 'facet' with its allowed values. The description clarifies that facet aggregates 'one field' but adds no format or syntax detail beyond the schema. 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 specific verb and resource: 'Returns terms-aggregation counts for one field over the Goodreads authors dataset.' It distinguishes itself from the search sibling by calling out 'the related search tool,' though it doesn't name the exact sibling tool. An agent can tell it is a facets/aggregation tool rather than a list tool.

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?

Explicitly frames usage: 'Use alongside the related search tool to inspect filter counts under the same query filters.' This gives a clear when-to-use context and pairs it with search, but does not state when-not-to-use or name the sibling explicitly.

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