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

Goes well beyond the annotations: it discloses the pricing model ($0.003/call via x402 USDC or card key, first 25 free, failed calls free) and proactively reconciles the surprising readOnlyHint=false by stating 'Reads or computes only; not marked read-only because each call is charged.' This is exactly the context an agent needs and cannot infer from structured fields.

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?

Front-loads the resource and returned fields, then usage, then pricing/auth. Dense but every clause carries information; the parenthetical price/auth sentence is long but earns its place for a paid tool.

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?

No output schema exists, and the description compensates by enumerating the return fields explicitly, including the population year. Combined with the pricing, auth, and read-only rationale, an agent has everything needed to decide and invoke correctly for a one-parameter open-world 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 coverage is 100% and the single parameter's schema description already says 'ISO 3166 alpha-2 or alpha-3 code', so the baseline is 3. The description adds the useful examples (SE, SWE, US) that concretely demonstrate both code formats, but no additional syntax, case, or validation semantics.

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+resource ('Facts about a country by ISO code') and enumerates the exact fields returned: World Bank name, ISO-2/ISO-3 codes, region, income level, capital plus coordinates, and population with year. Nothing in the sibling list (earthquakes, weather, holidays, etc.) overlaps, and the source ('World Bank open data') is named.

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?

Gives explicit intent ('Use to enrich records with country data') and a concrete invocation example ('country=SE'). It does not name when-not-to-use or an alternative tool, but the sibling set contains no competing country-data tool, so the omission is low-cost.

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