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

Annotations already declare this is a safe read (readOnlyHint=true, openWorldHint=false), so the description's job is to add domain context — which it does well, defining the three status categories and the one exclusion (another player's capital is unavailable). It does not describe result ordering, pagination, or how much detail accompanies each country, leaving a small gap.

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 dense sentence that front-loads the scope (all 173 countries) and then enumerates the meaningful distinctions. Nothing is padded or repeated from the schema.

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 one-parameter read-only listing tool with full schema coverage and no output schema, the description supplies the domain vocabulary an agent needs to interpret results. Minor incompleteness: it does not state the shape of an entry or confirm the default filtering behavior in prose.

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 description coverage is 100% for the single boolean onlyAvailable, so the schema already carries the parameter meaning. The description never references the filter directly, though its closing line about unavailable capitals loosely gestures at what availability means; baseline 3 applies.

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' + 'all 173 countries') and immediately explains what each entry conveys (joinability status: free, AI-run, occupied). It implicitly separates itself from my_nation by scoping to all countries rather than the caller's own, but never names that sibling explicitly.

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: an agent can infer this is the discovery step before joining or taking command of a nation. There is no explicit when-to-use, no when-not-to-use, and no named alternative among the siblings (my_nation, briefing, rules).

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