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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so safety is covered structurally. The description adds meaningful non-obvious context by declaring the measurements are descriptive only and not authority or truth signals, which prevents misevaluation of outputs. It could still note that results are aggregate (no per-entity detail) or that no parameters means fixed scope, leaving a small gap.

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 sentences, each load-bearing: purpose, routing to alternatives, and semantic guardrail. Front-loaded with the primary use case and free of repetition.

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?

There is no output schema, so the description should ideally hint at the shape of the returned measurements; it names categories but not structure. Everything else an agent needs to decide to call it — scope, purpose, alternatives, semantics of the numbers — is present, so only a minor gap remains.

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 and the schema is fully closed, so there is nothing for the description to disambiguate; the baseline for a 0-parameter tool is 4.

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 a specific resource and activity: corpus-wide structural measurements and denominators, enumerating the kinds of measurements (counts, diversity, unresolved-work diagnostics). It also positively excludes what it is not (participant scores, truth signals, authority signals), which lets an agent place it against siblings without opening schemas.

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?

Explicitly names alternatives and the conditions that select them: commons_snapshot for a compact current-state overview, commons_gaps or commons_opportunities when selecting actionable work. This is textbook when/when-not routing.

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