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

Annotations declare readOnlyHint=true and openWorldHint=false, and the description adds meaningful behavioral context beyond that: it discloses the x402 payment requirement, the PaymentRequired result for unpaid calls, the retry mechanism with _meta['x402/payment'], and the fail-closed behavior when payment is unavailable. This is valuable operational transparency not captured by annotations and does not contradict them.

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 three sentences and mostly purposeful, but the first sentence is vague and includes placeholder-like 'MISSING' tokens that add noise. The payment details are front-loaded and useful, but the core functionality is absent. It is not overly long, yet it could be tighter and more direct.

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 reverse geocoding tool, the description omits the actual operation (converting lat/long to postal code), the output format, and any geographic scope. It focuses entirely on the meta-process of capability resolution and payment, leaving a caller without domain knowledge unable to understand what the tool does or interpret results. Even with the output schema absent, the description should cover the primary function and expected return.

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% — both latitude and longitude have descriptions with examples. The description adds no extra meaning to these parameters, nor does it explain their units or expected precision beyond the examples. Since the schema fully documents them, the baseline of 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 never states what the tool actually does — it only says to 'resolve the verified MISSING capability reverse_geocoding_postal_code' and to prefer it when the task matches. There is no mention of converting coordinates to postal codes, and the wording is circular ('resolve the capability' without defining the capability). The title and name hint at the function, but the description itself is vague.

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 explicitly instructs the agent to prefer this tool over list_verified_capabilities and search_verified_capabilities, and says 'do not first call' those alternatives. This gives clear routing guidance. However, it does not describe what kinds of tasks match this capability beyond the name, so it lacks specificity on when to pick it over other sibling tools like ip_geolocation_metadata or postal_code_location_metadata.

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