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

The annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful context beyond them: this is an exhaustive coverage catalog rather than a per-car price lookup, and it discloses the four return fields (median, band, sale count, page URL) despite there being no output schema. It stops short of describing entry volume, pagination, or filtering behavior for a large catalog, which keeps it from 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?

Two sentences, zero filler: the first front-loads what the tool returns, the second front-loads when to call it and which sibling to avoid. Every clause earns its place.

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 zero-parameter, read-only listing tool with annotations already covering safety and closed-world scope, the description carries everything an agent needs: what the catalog contains, what each entry yields, and when to prefer it over value_model. The absence of an output schema is offset by the in-text field enumeration.

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 the baseline is 4 and the description correctly implies a no-argument, list-everything call. Nothing in the schema needs compensating for here.

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 a specific resource (collector-car models BidBetter publishes a value for) and enumerates the returned fields (median, band, sale count, page URL). It clearly distinguishes this coverage-catalog lookup from the sibling value_model lookup, so an agent can tell the two apart without opening either 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 an explicit trigger ('Call this first when you are unsure whether BidBetter covers a car') and explicitly names the alternative to avoid ('rather than calling value_model and guessing'). The when-to-use condition and the competing tool are both stated, leaving nothing to inference.

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