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

Beyond the annotations (readOnly, idempotent, non-destructive), the description discloses ranking integrity ('never by who pays'), data freshness ('when the price was checked'), return fields (store, price, shipping, buy link, ranking rationale), and a graceful degradation behavior. Since no output schema exists, this disclosure of return content is doing real work.

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 sentences, front-loaded with what the tool does and how it ranks, with coverage caveats trailing. Slightly dense in the middle sentence, but every clause — trust signal, return fields, category coverage, fallback behavior — 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?

With no output schema, the description compensates well by naming the returned fields and the failure mode for unsupported categories. Minor gaps remain, such as how many options are returned or whether results are cached vs. live, but nothing critical for correct invocation 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?

Schema description coverage is 100% and both parameters are documented with examples and an enum, so the schema already carries parameter meaning. The description adds no per-parameter guidance, which is acceptable at this baseline but not value-adding.

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 gives a specific verb ('Find'), resource ('best real options to buy a product'), and the ranking principle that defines the tool ('ranked only by what is best for the buyer'). It also enumerates the return payload, so an agent knows exactly what it gets back without consulting 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 states applicability clearly ('any product sold online in the US') and, importantly, the condition under which it should not be relied on ('if a category is not compared yet, it says so instead of guessing'). It does not, however, route the agent to or away from the sibling tool price_history, which would have made the guidance complete.

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