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

With no annotations, the description carries full burden. It discloses the payment dependency (+ x402 authorization) and the conditional response behavior (paid response vs 402 accept-list). It adds value beyond the schema by explaining the tool's operational context, though it omits details like rate limits or data freshness.

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 with no redundant phrases. It efficiently conveys purpose, payment flow, and state without payment. However, the sentence on pricing could be integrated more succinctly.

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?

The description lacks output schema and only vaguely describes the return as 'normalized address + place class/type.' The structure of the 402 accept-list response is not detailed. Given no output schema, the agent would benefit from more explicit return format and limitation context.

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%, but the description adds meaning beyond parameter names. It explains that 'lat' and 'lon' are WGS84 coordinates for reverse geocoding toward a normalized address, and it clarifies the '_payment' parameter's role in the x402 payment flow. This significantly aids parameter understanding.

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 explicitly states 'Reverse geocoding via OpenStreetMap Nominatim' with a clear verb-resource pair. The phrase 'lat/lon → normalized address + place class/type' specifies the input-output mapping. Given sibling 'osm_geocode' likely does forward geocoding, this tool is well-distinguished.

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 clearly explains when to include the '_payment' argument to unlock paid response and what happens without it. It provides context for the payment flow but does not explicitly state when to choose this tool over alternatives like 'osm_geocode' or when not to use it.

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