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

With no annotations, the description carries the full disclosure burden. It adds one genuinely useful behavioral fact — calls are metered and limited to 5 free trials per registered wallet — but says nothing about required auth, input format constraints, idempotency, or what the response looks like.

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 short clauses with the core function front-loaded. The leading 'x402-country:' name-echo is redundant and the emoji is decoration, but nothing else is wasted; it is appropriately compact for a simple lookup.

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 tool with no output schema and no annotations, the description is expected to carry the input-format and return-value explanation. It states neither which ISO standard is accepted (e.g., ISO 3166-1 alpha-2 vs alpha-3) nor what the tool returns, so an agent cannot predict the invocation result.

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%, triggering the baseline of 3, but the schema descriptions are tautological ('Iso to process', 'Code to process', 'Country to process'). The description adds marginal value by hinting that iso is the primary input, but never explains whether the three params are aliases, alternatives, or each maps to a distinct query mode — leaving the agent to guess which to populate.

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?

'Country by ISO code' names the resource and the operative input, so an agent can tell this is a country-lookup tool — more than a tautology. But it is a verbl-less noun phrase, does not state what the tool returns (country name? details? flag?), and never differentiates itself from overlapping siblings like x402-country-code and x402-country-brief.

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?

No guidance on when to pick this tool over the many country-adjacent siblings (x402-country-code, x402-country-brief, x402-capital-city, x402-currency-by-country). The '5 free trial calls' note is a metering/cost signal, not a selection rule; when-to-use must be inferred entirely from the name.

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