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

Annotations already cover safety (readOnly, idempotent, non-destructive), so the bar is lower. The description still adds a genuinely useful behavioral caveat — 'most cities have none' — warning the agent that empty results are the norm and not an error, plus a hint about what the returned value is used for.

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 short sentences, zero filler, with the scope qualifier front-loaded and the follow-up usage note second. Everything earns its place.

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?

With no output schema, the description carries the burden of saying what comes back (district slugs with active listings) and it does, plus the empty-result caveat. It stops short of describing the response shape (e.g. slug+name fields), which is a minor gap for a two-parameter list tool.

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?

Schema coverage is 100% and both parameters are fully documented in the schema (city slug from list_cities, country code/region format). The description only references the output field `district`, not the inputs, so it adds little beyond the schema — baseline 3.

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 districts of a city) plus a scoping qualifier (only those with active listings). This clearly separates it from list_cities and list_countries, which operate at different geographic levels.

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 a forward-pointer to the downstream tool: use the returned slug as `district` in search_listings, which tells the agent why it would call this. It lacks an explicit 'do not use this for X, use Y instead' clause, but the sibling set is small and the purpose is unambiguous.

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