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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, but the description adds operational facts the annotations cannot convey: it is keyless, free, and consumes no quota, and it is safe as a cheap liveness probe. It also bounds the output scope ('says nothing about any specific country pair'), preventing a wrong-tool expectation.

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?

Three short sentences: what it returns first, scope boundary second, invocation conditions and cost third. Every clause carries information an agent needs, and nothing is repeated from the schema or annotations.

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 zero-parameter, read-only stats tool with no output schema, the description covers the returned metric categories, the cost/auth profile, and the sibling boundary. There is no material gap an agent would need filled before calling it.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; the baseline for a parameterless tool applies. The description correctly implies a no-argument call without adding spurious input guidance.

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 first sentence names the specific resource (the Orizn visa database) and enumerates exactly what is counted: pairs, passports, destinations, enriched records, translations and languages. The second sentence explicitly demarcates it from the sibling tools quick_visa_check and check_visa_requirement, so an agent can route without inspecting either schema.

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?

It states both when to use it (user asks how complete the data is, or as a reachability pre-check before a longer session) and when not to (anything about a specific country pair, with the two alternatives named). This is the explicit when/when-not/alternatives pattern.

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