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

The description clearly conveys a read-only count operation and discloses the output breakdown, which is the main behavioral trait for a zero-argument stats tool. It does not mention caching, freshness, or access constraints, but with no annotations the core read-only behavior is still clear from 'How many... currently indexes'.

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 front-loaded sentence with no filler. It states the metric, the resource, and the grouping dimension efficiently, earning its place entirely.

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?

With zero parameters and an output schema present, the description plus schema is nearly sufficient to invoke the tool correctly. The main missing piece is explicit guidance on when to prefer this tool over its siblings, though that gap is already reflected in usage_guidelines.

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 input schema is empty and schema coverage is 100%, so there are no parameter semantics for the description to add. A zero-parameter tool gets a baseline of 4, and the description appropriately focuses on output rather than arguments.

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 identifies a specific resource ('listings Clearhouse currently indexes'), the metric ('How many'), and the grouping ('by source registry'). This makes the tool's purpose unmistakable and clearly separates it from operational siblings such as call_service and quote_call.

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 gives no explicit guidance on when to use index_stats versus search_agents or the other siblings. There are no triggers, exclusions, or alternative tool references, so the agent must infer usage from the name and wording alone.

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