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

Annotations already declare readOnlyHint=true, openWorldHint=false, destructiveHint=false, so the safety profile is covered. The description adds the otherwise-missing return field list (type, description, page count, main pages), which is genuinely useful given there is no output schema. It has no params, so it is effectively scoped to one fixed site, though that is left implicit.

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 short sentences, each doing work: what it returns, which fields, and when to call it. Front-loaded with the return value and no filler.

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?

Adequate for a parameterless, read-only inspection tool whose annotations cover safety and which helpfully lists its return fields in absence of an output schema. It could note that the tool is bound to a single predetermined site, but an agent can operate it correctly as written.

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?

Zero parameters, so the baseline of 4 applies. Schemas coverage is 100% and there is nothing extra for the description to explain.

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 concrete verb (return info about a site) and enumerates the specific content returned: type, description, loaded-page count, and main pages. This distinguishes it in effect from fetch/get_page/list_pages/search, though it never names a sibling explicitly.

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?

"最初にサイトの全体像をつかみたいときに使います" gives a clear triggering condition (first, whole-site orientation). It offers no exclusions or named alternatives, so it stops short of a 5.

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