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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered without the description's help. The description adds genuine value beyond that by disclosing the payload contents, namely the host_id identifier and each site's verification status. It does not say what happens with an empty account or how many sites are returned, but for a parameterless read-only list those gaps are minor.

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?

One short sentence with no wasted clauses, and the most actionable detail (host_id for downstream yandex_* calls) is included up front. It is a sentence fragment without a leading verb, which slightly weakens scannability but does not obscure meaning.

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?

For a zero-parameter, read-only discovery tool with no output schema, the description covers the essentials: what is returned, the field needed by sibling tools, and the verification flag. It stops short of describing return shape or ordering, but with no output schema and a trivial input surface there is little else an agent needs to call it correctly.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; the baseline for a 0-param schema applies. The description instead spends its words on identifying the key output field (host_id), which is the more useful information here.

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 names a specific resource (sites in the user's Yandex Webmaster account) and scopes it to the Yandex platform, which lets an agent distinguish it from gsc_list_sites and bing_list_sites in the sibling list. It is a noun phrase rather than a verb+resource statement, so the action ('list') is only implied by the tool name.

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 phrase 'the host_id other yandex_* tools need' implicitly tells the agent to call this first as a prerequisite for yandex_site_summary, yandex_list_sitemaps, yandex_search_queries and similar tools. However, there is no explicit when-to-use statement and no explicit exclusion naming gsc_list_sites or bing_list_sites as the alternatives for other platforms, so the routing guidance must be inferred.

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