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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered, and an output schema exists to carry the return shape. The description adds the useful behavioral fact that facets honor the same filters as search and return counts rather than listings, but does not elaborate on cardinality, pagination of facet values, or error behavior.

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 short sentences, front-loaded with the core purpose, and every clause carries information (aggregation counts, same-filters behavior, pairing with search). Only minor jargon ('terms aggregation') slightly reduces immediate readability.

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 annotations covering safety, a 100%-covered schema, and an output schema describing return values, the description supplies what structured fields cannot: that counts are computed under the same filters as search and that it is meant to be used alongside search. Sufficient for correct invocation, though it could note the required facet more explicitly.

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% across all 23 parameters, so the schema already carries full parameter semantics. The description adds nothing about the required 'facet' argument or its allowed values, leaving the schema to do all the work — appropriate baseline 3.

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 the vehicle listings dataset'), which differentiates it from the item/search/price_history siblings. It implies the facet-counts nature clearly, though it never names search/item siblings directly.

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?

Gives clear usage context ('Use alongside the related search tool to inspect filter counts under the same query filters'), telling the agent this is a complement to search rather than a standalone listing retrieval. No explicit when-not guidance, but the intended pairing is unambiguous.

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