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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile needs no restating. The description adds genuinely useful behavior beyond that: results are localized to the requested language and tags come back ordered most-used-first, which matters for choosing filters. It stops short of explaining volume or limits, but no output schema exists and the return contents are otherwise well characterized.

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 payload is front-loaded into the first sentence, with the routing guidance following in priority order. Dense but readable; the closing easy_to_memorise tip is slightly tangential yet still actionable for an agent, so it earns most of its space.

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?

A one-parameter, read-only reference tool with no output schema demands that the description explain what comes back — and it does, down to the fields (mood names, tag ordering, collection title and slug). Nothing essential for calling it correctly is missing.

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?

With one parameter at 100% schema coverage and a fully enumerated ISO code list plus default, the schema carries essentially all parameter semantics. The description only reinforces that the returned names are in that language, a marginal but real addition beyond the enum itself.

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 names the resource precisely: the facet vocabulary available for one language — the 8 moods, the most-used tags, and collections with title and slug. That enumeration makes it immediately distinguishable from data-returning siblings such as find_poems and get_collection, which it explicitly routes to.

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?

It gives explicit when-to-use routing: call this to narrow find_poems using one mood plus 1–3 tags, or to pick a collection for get_collection. It even supplies a concrete recipe (easy_to_memorise for a first poem), so the agent knows both the trigger and the downstream call shape.

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