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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety/freshness profile is covered externally. The description adds no behavioral context beyond confirming it is a fetch (e.g., no rate limits, caching, or data-granularity notes), which is acceptable but thin given annotations do the 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?

Two tight sentences with no waste, and the core action is front-loaded ahead of the routing hint to the sibling tool.

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 needn't be described, and annotations cover safety. For a single-parameter fetch tool this is essentially complete; only minor detail like domain input formatting is absent.

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% for the single `domain` parameter, so the schema already documents it. The description adds no format guidance (e.g., whether to pass 'example.com' vs 'https://www.example.com'), so baseline 3 applies.

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 (Fetch), resource (Similarweb traffic and engagement data), and scope (a specific `domain`). The sibling `similarweb_search` is explicitly named and contrasted, so an agent can differentiate the two without opening schemas.

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?

Directly names the alternative tool and the condition that selects it: use similarweb_search to discover or compare domains, implying this tool is for when a domain is already known. Nothing 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.