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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds the 2–20 input range and a disclaimer about interpretation, but says nothing about rate limits, cross-retailer availability, or how the evidence score is derived.

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 tight sentences, zero filler, with the scope and ranking behavior front-loaded and the caveat last. 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 read-only tool with no output schema, the description should describe what comes back; "rank them by marketplace-evidence score" hints at ordering but not the response shape or how many results return. Adequate but with a clear gap on return values.

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?

Top-level schema coverage is 0% for the single `products` parameter, so the description carries some burden; "2–20 retailer listings" conveys the array shape and cardinality. However, the nested retailer/product_id fields are documented in the schema, so the description adds only marginal value beyond it.

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 verb (compare) and resource (2–20 retailer listings) and states the ranking basis (marketplace-evidence score). It is distinguishable from siblings like check_store_score and check_product_trust by resource, though it never names or contrasts them explicitly.

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?

"This is not purchase advice" sets a useful boundary on interpretation, but there is no positive guidance on when to reach for this tool versus check_product_trust or check_store_score. Usage is implied rather than stated.

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