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

Annotations cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds material context beyond them: it enumerates what is returned (editorial fit, caveats, price scope and dates, warranty, recalls, sponsorship disclosures) and gives a domain caveat that brand ranges may be heater-only or portable rather than installed-sauna prices. This is exactly the kind of presentation constraint an agent could otherwise get wrong.

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 the action and cardinality, then the return payload, then the slug source and the pricing caveat. No filler; the dense return enumeration is justified because there is no output schema.

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 must describe return values and does so explicitly, and with a single simple array parameter the input side needs little more. The added warning about heater/portable price scope closes the main remaining ambiguity for an agent summarizing results.

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 0%, so the burden falls on the description, which does compensate meaningfully: it specifies that slugs must be exact Sauna Guide slugs, constrains cardinality to two or three brands, and names the tools/directories that produce valid slugs. It does not restate the lowercase-hyphen pattern, but that is visible in the 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 and resource ('Compare two or three brands') plus the exact identifier type needed ('exact Sauna Guide slug'), which immediately separates it from find_sauna_brands (discovery) and estimate_sauna_total_cost (pricing math). The cardinality constraint (two or three) is stated up front.

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?

Explicitly routes the agent to find_sauna_brands or the brand directory for obtaining slugs, which is the key prerequisite. It does not, however, state when to prefer estimate_sauna_total_cost or check_sauna_quote instead, so no sibling exclusion beyond the slug source.

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