list_countries

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

No annotations are provided, so the description carries the burden. It discloses the return contents (ISO codes, both source names, currencies, World Bank match flag) but says nothing about permissions, whether the continent argument is case-sensitive, error behavior for unknown continents, or coverage limits for a read tool.

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 sentences, front-loaded with what is returned and followed by the question it answers. The trailing 'via countries_listed_by_source' is slightly noisy and slightly out of register with the rest.

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 correctly enumerates the returned fields, and with no annotations it covers the core read-only listing behavior. A brief note on continent name format or unknown-value handling is the only real gap for a single-parameter 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 description coverage is 0% and the only parameter has just a title, so the description must compensate. The example value 'EU' plus 'for a continent' gives meaningful guidance on the expected format, which is real added value, but nothing states accepted spellings or case handling.

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 gives a specific verb and resource ('List every country the source lists for a continent') plus the exact payload fields returned, which is more than enough to distinguish it from list_continents or get_country_metric. It stops short of naming a sibling it must not be confused with (e.g. region_total), so it doesn't reach a 5.

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 implied by the embedded question 'how many countries are in <continent>?', which tells the agent the scenario this satisfies. There is no explicit when-not guidance or pointer to an alternative aggregation tool, so it stays at the implied-usage level.

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