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

Goes well beyond the readOnlyHint annotation by explaining the x402 payment flow: unpaid calls get PaymentRequired, clients retry with _meta['x402/payment'], and the system settles via Kappa and fails closed if payment rail/economics are unavailable. This is precisely the kind of behavioral context agents need. The 'MISSING' in 'MISSING then verifies' is a template artifact but doesn't hide behavior.

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?

Purpose is front-loaded and the payment explanation is valuable, but the description contains an unresolved 'MISSING' placeholder and is somewhat verbose for a single-parameter lookup. It could be tightened without losing routing or payment context.

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 one-parameter read-only lookup with no output schema, the description covers the input semantics, the return intent (name and region), and the unusual payment behavior. It stops short of specifying the exact response shape or handling of invalid codes, but that is a minor gap given the tool's simplicity.

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 already covers the only parameter 100% with a description and example ('JP'). The tool description adds only the phrase 'alpha country code', which slightly reinforces the format but adds no new semantics beyond the schema.

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 the exact operation: look up a country's name and region from an alpha country code, so an agent can distinguish it from the discovery tools it names. The literal 'MISSING' placeholder in 'Use this direct MISSING tool' muddies the tool identity, and it does not contrast with other metadata lookup siblings.

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?

Explicitly says to prefer this tool and not to call list_verified_capabilities or search_verified_capabilities first, which is concrete routing. The phrase 'when the caller's task matches this capability' is somewhat circular, and no guidance covers invalid/unknown country codes or alternative country-data tools.

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