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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds some behavioral context by noting it aggregates in one call and reuses list_bookmarks filters, but it does not disclose deeper behavioral traits like performance characteristics or limitations. This is adequate but not rich beyond 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?

Three compact sentences with the core function front-loaded, followed by filter compatibility and usage guidance. There is no filler, repetition, or unnecessary detail.

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 that an output schema exists and annotations already cover read-only/idempotent behavior, the description is complete for the agent to invoke the tool correctly: it states what the tool returns, how filters behave via list_bookmarks, and when to choose it. Nothing essential is missing.

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 description adds cross-tool meaning by saying 'Accepts the same filters as list_bookmarks,' and it hints at relevant dimensions like favorite/untagged/note counts. However, schema coverage is only 50%, and the description does not explain the nested filter fields or mode enums, so it only partially compensates for the low coverage.

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 uses a specific verb and resource ('Aggregate counts over the user's library') and names concrete output dimensions: total, platform, content type, capture month, favorite/untagged/note counts. It also explicitly distinguishes itself from list_bookmarks by framing itself as the count/overview tool rather than a paging tool.

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?

It directly states when to use the tool: for 'how many' and overview questions. It also names the alternative approach—'instead of paging bookmarks'—which implicitly tells the agent not to use this tool when item-level details are needed.

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