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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuinely useful context that no annotation or schema conveys: it enumerates the returned coverage payload (per-axis, per-confidence, per-self-report, pre-canonical, unreviewed counts, and version stamps), which substitutes for the missing output schema.

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 compact sentence with the headline ('Coverage statistics') front-loaded and the detail carried in a semicolon list. Dense but every clause names a distinct returned metric, so nothing is wasted.

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 stats tool with no output schema, the description supplies the return-field inventory an agent needs to decide whether to call it. It stops short of explaining what 'pre-canonical' or 'pattern-layer versions' mean, which would help interpretation.

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 the baseline of 4 applies. The description correctly implies a no-argument, whole-corpus scope.

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?

States the specific resource (coverage statistics) and enumerates the exact axes it reports on, so an agent can tell it apart from the list_/get_ siblings that return records rather than counts. It never uses an explicit verb like 'returns' or 'report', but the intent is unambiguous.

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 statement of when to call this versus the sibling tools (list_axes, list_dysfunctions, render_pattern_review) or what question it answers. Usage must be inferred entirely from the field list.

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