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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description adds real behavioral context beyond them: unknown slugs yield a notFound list rather than an error, and priced plans carry a dated citation intended to be quoted verbatim — non-obvious traits an agent must know.

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 tightly packed sentences with zero waste, front-loading the core action and then the parameter guidance and return shape. Every clause carries information an agent would otherwise have to guess.

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 correctly fills the gap by describing the return payload (full provenanced records plus a notFound list) and the citation field. Both parameters and the theme/slug vocabulary are addressed, leaving no obvious omission for a read-only lookup tool.

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 coverage is only 50% (the `slugs` array has no schema description), so the description compensates by showing two concrete slug-array examples and clarifying that `section` accepts any of 275 theme slugs, not just the old four-section set. It adds genuine meaning beyond the raw schema.

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 ('Compare specific vendors side by side by slug') with an explicit scope constraint ('within any theme'), and the vendor framing implicitly separates it from the sibling compare_products. Concrete slug/theme examples let an agent recognize the target data immediately.

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?

Gives clear operational context: set `section` to the theme slug from list_sections, and names list_sections/list_coverage as the sources for valid slugs. It does not explicitly state when to prefer this over search_vendors or compare_products, so no exclusion criteria are given.

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