get_data_countries

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is fully covered. The description adds value the annotations cannot: it discloses the exact payload shape (all countries, ISO-2 codes, full names) and that no parameters are needed, which matters since there is no output schema. It stops short of mentioning caching, rate limits, or result size.

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?

It is well front-loaded with the Overview first, but for a trivial no-argument lookup the content is inflated into five markdown sections. 'What You Get' and 'Quick Start' restate the same facts (country list, ISO-2 codes, no parameters) already given in the Overview, so several sentences do not earn their 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?

For a simple read-only reference endpoint, the description covers purpose, use cases, returned fields, and the fact that no input is required. With annotations handling behavioral hints and no output schema to lean on, the description supplies nearly everything an agent needs; only caching/pagination-style operational details are absent, which is low impact here.

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 optional 'timeout' parameter, so the schema fully documents it and the baseline of 3 applies. The description's 'No parameters required' is consistent with the zero-required-parameter reality but adds nothing the schema does not already convey.

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 states a specific verb and resource ('Get a complete list of all countries... with their ISO-2 country codes') and names the returned data precisely. It is clear what the tool does, but it never explicitly distinguishes itself from the many sibling reference-data tools (get_data_cities, get_data_currencies, get_data_languages), so an agent must infer the boundary from the resource name alone.

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?

The 'When to Use' section gives four concrete scenarios (dropdowns, location filters, form inputs, reference data for other endpoints), which is solid context for an agent deciding when to reach for this tool. It offers no exclusions or named alternatives, so it stops short of the explicit when-not guidance that would warrant a 5.

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