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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered; the description adds real value with 'No sign-in needed' (auth context) and by enumerating the returned fields (name, biome, cell, wards), which matters because there is no output schema. It stops short of explaining what 'wards' or 'cell' contain or how the two identifiers interact.

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?

A single front-loaded sentence that defines the resource first and then the payload, with no filler. The only cost is jargon ('cell', 'wards') that a reader must already know.

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 only two fully documented parameters and annotations covering safety, the description compensates for the missing output schema by naming the return fields. What is missing is disambiguation from the city/town/map siblings, which matters in a 24-tool server.

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 the schema itself documents both slug and regionId including their provenance ('from list_regions'), so baseline 3 applies. The description adds no further meaning about identifier format or what happens if slug and regionId disagree.

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 concrete retrieval: a region's capital with its name, biome, cell and wards. The parenthetical 'a landmark that belongs to nobody' clarifies what a capital is here, but it never names the close siblings (get_city, get_town, get_region_map), so the agent must infer why it would pick this over those.

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?

Usage is only implied: fetch a region's capital, keyed by regionId and slug. There is no explicit when-to-use or when-not-to-use guidance relative to get_city/get_town, and the prerequisite source (list_regions) appears only in the schema, not the description.

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