List car makes of a market

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so safety is covered. The description still adds real value beyond them: 'Free, spends no quota' discloses a cost property no annotation carries, and the warning that `data` is untrusted listing text gives explicit prompt-injection handling guidance. The only shortfall is that it says nothing about result size or truncation behaviour.

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 short sentences, each earning its place: what is returned and how it is ordered, when to use it plus the source/quota facts, and the untrusted-data caution. The most actionable constraint (free, no quota) and the sibling link to search_cars are front-loaded rather than buried.

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?

For a three-parameter, read-only enumeration tool with full schema descriptions, complete annotations and an output schema, nothing essential is missing. Return shape is delegated to the output schema, safety to annotations, and the description covers the remaining gaps: quota cost, ordering, and untrusted-content handling.

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%, and the schema already documents the market enum values, the limit default/maximum and case-insensitive name_contains. The description's market-to-source mapping and 'most frequent first' ordering merely restate what the schema already states, adding no syntax or edge-case semantics on top. Baseline 3 applies when the schema does the heavy lifting.

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 names the resource (car makes/brands on sale), the scope (one market) and the ordering (most frequent first), plus which sources back each market. It also implicitly separates itself from search_cars by positioning the output as 'the spellings search_cars understands'. It stops short of a clean verb-first statement and never contrasts with list_models, so it is strong but not perfectly differentiated from all siblings.

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?

'Use it to see whether a make is available and how many cars it has' gives a concrete selection context, and the search_cars spelling remark tells the agent to consult this before searching. There is no explicit when-not-to-use or a named alternative such as list_models or get_markets, so the exclusions side is left to inference.

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