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 only that results are 'public' product results, and says nothing about result caps, pagination, ranking, or that a category slug can be obtained from costco_categories. Credit is limited because it contributes little behavior beyond the annotations.

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 waste. The purpose and input scope are front-loaded in sentence one, and the sibling-disambiguation routing follows in sentence two.

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?

An output schema exists, so return values need no explanation, and annotations carry the safety profile. The description is complete for selection and invocation, but for a search tool it omits any hint of result limits, ordering, or paging behavior, which the two-parameter schema cannot convey.

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 self-documented, so the schema does the heavy lifting. The description restates the parameters ('by `query` and/or a category slug') without adding format or constraint detail beyond what the schema already provides, which is the baseline-3 case.

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 ('Search Costco public product results') and immediately enumerates the two input modes ('by `query` and/or a category slug'). It names the three closest siblings and what each is for, so an agent can distinguish costco_search from costco_product, costco_categories, and costco_product_availability without opening any 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?

Explicit routing: 'Use costco_product for one product's details, costco_categories to discover category values, or costco_product_availability to check delivery stock.' It also states that query and category are combinable ('and/or'), which tells the agent both are optional. Nothing about alternative selection is left to inference.

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