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

The readOnlyHint annotation already covers the safety profile, and the description adds useful context about what dimensions are included. However, it does not disclose how freshness is computed, whether counts are approximate, or what the response structure looks like. This is a mild gap rather than a contradiction.

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?

A single sentence with a colon-separated list conveys the core value immediately and enumerates the four covered dimensions without any wasted words. It is appropriately concise and well structured.

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 parameterless, read-only stats tool, the description covers the essential purpose and content dimensions. Since there is no output schema, it leaves some ambiguity about the exact return format, such as whether results are per-site counts, global totals, or timestamps, but this is unlikely to prevent a correct call.

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 has zero parameters, so the schema already fully documents invocation needs. The description provides context about what the statistics measure, which is sufficient given no parameters exist.

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 identifies what the tool reports: corpus size and freshness across sites, pages, passages, and languages. It is specific enough to distinguish it from the search, fetch, and watch siblings, though it lacks an explicit action verb and does not directly contrast with related list/source 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?

No guidance is given on when to use index_stats versus alternatives like list_sites, source_profile, or search. The usage context is only implied by the name and description, with no explicit conditions, exclusions, or recommended alternatives.

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