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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so safety is covered; the description adds substantive context beyond that — that it benchmarks against actual recent sold prices, reports a % delta vs the sold median, and surfaces cheaper listings filtered by shipping to the buyer. It does not mention failure modes for unsupported links or rate limits.

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?

A single front-loaded sentence that leads with the core judgment task and then qualifies it with the comparison basis and the secondary output. Dense but every clause carries information; no filler.

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 rich annotations, full schema coverage and an output schema, the description covers what the tool does and how its verdict is derived, which is enough for correct invocation. Minor gap: no note on what happens with an unsupported or expired listing link.

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%, including the supported domain list and the ISO country code semantics, so the schema carries the parameter burden. The description adds only the concept of 'delivered price' and shipping relevance, which is already implied by the country parameter description, so baseline 3 applies.

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+resource ('Judge whether an eBay listing is a good price') and enumerates the concrete output verdicts (great / fair / above typical / overpriced) plus the comparison basis (recent sold median). It is clearly distinguishable from siblings by operating on a listing URL rather than a model, though it never names get_used_price or list_tracked_models as alternatives.

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?

'Judge whether an eBay listing is a good price' plus the schema note about 'the eBay listing link the user pasted' makes the trigger context clear: the user has a specific listing and wants a price verdict. No explicit when-not conditions or sibling routing are given, so it stops short of a 5.

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