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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so safety is covered. The description adds genuine value beyond that by disclosing the payload contents (categories, tags plus applicability rules, patterns with groups/rules, picks, and counts) — detail the annotations cannot convey.

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?

Two sentences, no filler. The enumeration of returned facet types comes first, and the practical routing hint to search_references/random_references filters follows. Every clause carries information.

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 reference-list tool with no output schema, the description supplies everything an agent needs: the full inventory of what is returned, the extra rule metadata embedded in tags and patterns, the presence of counts, and how the values are consumed downstream. Nothing material 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?

The tool takes no parameters, which is the baseline-4 case. The description correctly implies an unfiltered, complete enumeration ('every valid...'), confirming the agent does not need to supply any narrowing input.

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 opens with a specific verb and resource: 'List every valid category, tag ... pattern ... and editorial pick, with counts.' It enumerates exactly what the returned facets contain, including the rule metadata attached to tags and patterns, so an agent knows precisely what this tool produces.

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 explicitly states the downstream purpose: these are 'the ids accepted by the filters (including `pattern`) of search_references and random_references,' which tells the agent to call this before filtering via those siblings. It stops short of an explicit when-not-to-use or a statement of alternatives, so it lands at 4 rather than 5.

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