Get markets and data freshness

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

The annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds genuinely useful behaviour the annotations cannot convey: the call is free and consumes no quota, and the payload contains untrusted text that must not be treated as instructions. It does not describe pagination or result shape, but with an output schema present that burden is lower.

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?

The purpose and the market list are front-loaded in the first sentence, followed by the use cases and the cost note. The enumeration of four markets is slightly verbose but concrete, and no sentence is filler. The untrusted-data warning is well separated at the end.

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 parameterless read tool with a full output schema and complete annotations, the description covers everything an agent needs: what it returns, when to reach for it, that it costs nothing, and how to treat the payload. Nothing material is missing.

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; the baseline for a parameterless tool applies. The description instead spends its space on explaining what the response fields mean, which is useful even though the schema is fully covered.

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?

A specific verb implied (list/describe) plus the exact resource: every market, and it enumerates the actual markets (Encar, Che168, Copart, IAAI) and the per-market fields returned (last update, age, staleness, active car count, plan inclusion). That level of detail lets an agent distinguish this from get_usage, which covers quota rather than market availability.

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 names two concrete triggers: 'how fresh is the data' and 'which markets can I use', which is clear when-to-use guidance. It also signals cost ('Free, spends no quota'), which quietly routes an agent here instead of a quota-consuming search. It stops short of explicit exclusions or naming the sibling to use instead for related questions.

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