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

Annotations already set readOnlyHint=true, and the description adds valuable behavioral context beyond that: it warns that the listing is exhaustive and can be a hundred-odd values, guarantees that every returned value is directly acceptable by scope_signals, and explains that place facets are gazetteer IDs with human-readable labels. This sets expectations for length and response content.

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 description is multi-sentence, but each sentence earns its place: purpose, guarantee of compatibility, length warning, routing to the alternative, and the place-ID caveat. It is front-loaded and free of tautology, making even the lengthy-warning meaningful rather than redundant.

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 tool with no output schema, the description fully compensates: it states exactly what the response contains, how long it can be, how the tool fits into the wider API, and how to use the results with scope_signals. The agent has enough context to invoke the tool correctly and interpret its result confidently.

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 input schema has zero properties and no required fields, so there are no parameters to explain. The baseline for 0 params is 4, and the description rightly does not invent parameter guidance. It further mentions the output structure enough for the absence of parameters to be non-blocking.

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 the full filter vocabulary'), explicitly enumerates all covered keys, and describes the exact output shape (flat list with a signal count each, plus a human-readable label for place ids). It also distinguishes itself from get_facet_manifest by naming itself as the exhaustive listing, so an agent can tell them apart without looking at any schema.

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?

The description gives explicit when-to-use/when-not-to-use guidance: use get_facet_manifest when only a domain and topic are needed to save tokens, and list_facets when the manifest lacks a value or counts are needed. It also instructs how to handle place facets (filter by name via scope_signals, not by raw id), which preempts a likely error.

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