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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and a closed-world scope, so the safety profile is covered. With no output schema, the description adds real value by disclosing the return content (counts of centers, places, categories) and data-freshness information ('when the data last changed'), though it does not specify the response shape or caching behavior.

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, front-loaded sentence that delivers the tool's purpose, scope, and return content with no wasted words.

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 aggregate tool with no output schema, the description is nearly sufficient: it names what is counted and notes freshness. A minor gap is that sibling list_sources exists, but the description does not clarify whether source counts are included or intentionally excluded.

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 is 4. The description correctly implies no filtering options are accepted, and there is nothing in the empty schema that the description needs to compensate for.

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 verb ('Get the number of') and precise resources (published psilocybin centers, places, categories, plus last-changed timestamp). This clearly distinguishes it from the sibling list_*/search_* tools, which return actual records rather than aggregate counts.

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?

Usage is implied: an agent can infer this is the aggregate/count tool to use instead of list_categories, list_places, or search_listings. However, the description never explicitly says when to prefer it over those siblings, nor does it state any exclusions or prerequisites.

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