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

Beyond the readOnlyHint annotation (which the description supports), it discloses the x402 payment requirement, the PaymentRequired on unpaid calls, and the fail-closed behavior. This is valuable behavioral context not available from annotations or schema. No contradiction with annotations; readOnlyHint is corroborated by 'look up' semantics.

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?

The description is well-structured: purpose first, then usage guidance, then payment specifics. Each sentence contributes meaningful information, though the phrase 'canonical Kappa financial engine' and 'MISSING' placeholders add minor noise. It is slightly verbose but not wasteful.

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 low-complexity tool (two simple string parameters, no output schema), the description covers purpose, usage guidance, payment behavior, and safety (read-only via annotation). It could mention the return format more explicitly, but 'place and coordinate metadata' is reasonably informative given the tool name and title. It is adequate for an agent to call it correctly.

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 description coverage is 100%: both postal_code and country_code have explicit descriptions and examples in the schema. The description adds nothing semantically beyond restating that these are a country and postal code, so no value is added 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 states a specific verb ('look up') and resource ('place and coordinate metadata') derived from a country code and postal code. It explicitly identifies itself as 'this direct MISSING tool' and contrasts with discovery tools, making its purpose distinct from siblings like list_verified_capabilities.

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?

The description gives explicit when-to-use guidance ('Prefer this tool when the caller's task matches this capability') and when-not-to-use ('do not first call list_verified_capabilities or search_verified_capabilities'). It also explains the payment retry flow, giving clear operational context for when an x402-capable client should invoke it.

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