Get allowed filter values

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

Annotations already declare readOnly, idempotent, open-world and non-destructive, so the safety profile is covered. The description adds two genuinely non-obvious facts beyond them: the call consumes no quota, and the `data` payload is untrusted listing text that must not be treated as instructions — a meaningful prompt-injection warning. It does not cover auth or rate limits, keeping this short of a 5.

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, front-loaded with what the tool returns, then how to use it, then the trust caveat. No filler or repetition of the title.

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 shape needn't be described, and the description instead supplies the two things the schema cannot: quota cost and the untrusted-data handling rule. That is complete for a zero-parameter lookup tool.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline is 4. The text compensates usefully by explaining what the returned keys mean and where they are consumed.

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 exact resource (canonical dictionary values) and enumerates the fields covered — fuel, transmission, drive, body_type — which distinguishes it from siblings like list_brands and list_models that cover different vocabularies. An agent knows precisely what it will retrieve without opening a schema.

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 downstream usage: 'Use the keys as the fuel, transmission and body_type filters of search_cars,' tying the tool to a specific sibling's arguments. It also states the cost profile ('Free, spends no quota'), though it doesn't spell out the trigger condition (call this before filtering) or any when-not case.

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