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

Annotations already provide readOnlyHint, openWorldHint, idempotentHint, and destructiveHint. The description adds behavioral context beyond annotations: default grouping, meaning of total field, metrics location under base. No contradiction with annotations.

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?

The description is a single dense paragraph without wasted words. It could benefit from slight restructuring (e.g., bullet points for parameter guidance), but the content is efficient and front-loaded with core purpose.

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?

Given 11 parameters, no output schema, and rich annotations, the description covers key behavioral aspects (grouping, total, metrics). It lacks details on pagination beyond autoPaginate hint, but overall provides sufficient context for an agent to use 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?

Schema description coverage is 100%, so baseline is 3. The description adds value by explaining the default period, the total field, and examples for sortBy (e.g. base.spent). This improves clarity 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?

The description clearly states 'Fetches performance statistics from the VK Ads v3 statistics service for ad plans, ad groups or banners.' It uses a specific verb ('fetches'), identifies the resource ('performance statistics'), and distinguishes from sibling tools that are CRUD or info retrieval tools.

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 description provides usage guidance on period grouping ('by default the grouping is `summary` — one aggregated row per object over the whole period; use day/week/month ONLY for daily dynamics or trend questions') and explains sorting and total field. Though it doesn't explicitly state when not to use this tool vs alternatives, the context of siblings (mostly CRUD) makes this clear enough.

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