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

Annotations already cover the safety profile (readOnly, idempotent, non-open-world), so the bar is lower, but the description still adds real context: coverage is honest and a destination appears only with a real, maintained directory. It goes beyond structured fields by disclosing the completeness guarantee of the result set, though it says nothing about result size or pagination.

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?

Three short sentences, each doing distinct work: what it returns, when to call it, and why the data is trustworthy. The most actionable instruction ('Call this FIRST') is front-loaded ahead of the justification.

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?

The tool is trivial to invoke (no params, no output schema), and the description compensates for the missing output schema by describing what comes back: destinations plus verified-place counts. No agent-relevant gap remains.

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?

Zero parameters, so the schema imposes no semantic burden and the description has nothing to disambiguate. Baseline 4 applies; there is no parameter detail the description fails to supply.

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 and resource (list which destinations Num covers) and adds scope detail: the count of verified places in each. It is clearly distinguishable from siblings like search_places, which it explicitly positions against as the cheaper alternative.

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?

Gives an explicit trigger — 'Call this FIRST when you do not know whether a city is supported' — and names the alternative behavior it replaces ('cheaper than a failed search'), which tells the agent when not to bother going straight to search.

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