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

With readOnlyHint=false, openWorldHint=true, idempotentHint=false already declared, the description adds the crucial missing context: it costs $0.001 USDC on Base per successful call via x402, which explains why a fact-lookup is flagged non-read-only and non-idempotent. Disclosing the World Bank data source and 'latest figure with its year' further clarifies freshness. Only minor gaps (failure/refund behavior) remain.

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 tight sentences, purpose front-loaded and the field list justified because no output schema exists. The parenthetical examples and source attribution are efficient, though the enumerated return fields make it slightly dense.

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 usefully enumerates return fields, and it documents the sole parameter plus the payment model, which resolves the otherwise puzzling non-read-only annotation. Complete enough for a one-parameter lookup, though it omits any error/retry behavior for the paid call.

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 schema already states 'ISO 3166 alpha-2 or alpha-3 code'. The description's examples (SE, SWE, US…) merely illustrate the same accepted formats, adding marginal value over the schema. Baseline 3 is appropriate.

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 opens with a specific verb+resource ('Facts about a country by ISO code') and enumerates exactly what comes back: World Bank name, ISO-2/ISO-3 codes, region, income level, capital coords, and latest population with year. An agent can distinguish this from data siblings like geocode or ip_info immediately.

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?

'Use to enrich records with country data' gives an implied use case but no when-not guidance and never points to an alternative sibling (e.g., wikipedia for narrative facts, geocode for coordinates). Usage is inferable but not routed.

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