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

Annotations already mark the tool as read-only, open-world, idempotent, and non-destructive. The description adds valuable behavior beyond that: output can be long (hundred-odd values on a busy wire), every returned value is currently accepted by scope_signals, and place facets are gazetteer ids. No contradiction with annotations.

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 front-loaded with the core purpose and uses a second paragraph for usage guidance. Each sentence adds value—warning about length, routing to get_facet_manifest, and explaining place id handling—though it is somewhat longer than strictly necessary.

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 tool with no output schema, the description covers result shape (flat list, counts, labels), the scope of keys, token-cost warning, and integration with scope_signals. This fully equips an agent to call it correctly without additional inference.

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?

There are zero parameters and schema coverage is 100% (empty object), so the baseline is 4. The description adds no parameter meaning because none exist, and instead focuses on output semantics, which is appropriate.

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 explicitly states the tool lists the full filter vocabulary and enumerates all keys (lang, country, region, domain, topic, severity, provider, coverage, place). It also specifies the output shape (flat list with signal counts and human-readable labels for place ids), which clearly separates it from siblings like get_facet_manifest.

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 routing guidance: use get_facet_manifest when only a domain and topic are needed, and list_facets when needing values not in the manifest or counts behind them. It also instructs to use scope_signals for filtering place facets by name instead of raw ids.

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