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

Annotations already provide readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe read operation. The description adds beyond that by disclosing that the tool will refuse (not answer misleadingly) if products lack a shared category, which is a behavioral trait not captured in annotations. A 4 is appropriate as it adds meaningful context without covering all possible edge cases.

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: the first states the core action, and the second provides a crucial constraint. Zero wasted words, front-loaded with purpose, and every sentence 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?

Given the tool's low complexity (1 parameter, 100% schema coverage, no nested objects, clear annotations, and an output schema), the description is complete. It covers the purpose, constraints, and refusal behavior, leaving no significant gaps for an agent to misinterpret.

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% (the 'slugs' parameter is described as 'Product slugs to compare'), so the baseline is 3. The description adds minimal extra meaning beyond the schema, only implying that slugs must be from a shared category. The description does not elaborate on format or validation, but the schema is sufficient.

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 uses a specific verb ('Compare') and resource ('two to five products side by side'), clearly distinguishing it from siblings like 'get_product' (single product) and 'search_products' (search). It also explicitly states a constraint: they must share a category, preventing confusion with cross-category queries.

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?

The description explicitly states when to use this tool (compare 2-5 products) and when not to use it ('a mixed request is refused'), providing clear exclusion criteria. It also references sibling behavior implicitly by noting that comparing across boards is meaningless, helping the agent avoid misuse.

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