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

With no annotations present, the description carries the full burden and does substantial work: it discloses the paid model ($0.005 USDC per call via x402 and the _meta["x402/payment"] field) and the sample=true free 3-row preview cap. That is exactly the kind of cost/side-effect context an agent needs before invoking. It says nothing about rate limits, error behavior, or response shape.

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 in the first sentence, followed by audience, then route/parameter reference, then payment terms — a sensible ordering. The route list is dense but each token is load-bearing. Slight cost: the route grammar strings are hard to parse on a single line and the 'travel apps, local-discovery apps, maps, games' audience list is marketing filler.

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 multi-route gateway with nested `params`, no output schema, and no annotations, the description covers purpose, route selection, per-route parameters, and the paid/free-preview mechanics — enough to call it correctly. Missing only return-format expectations and what errors look like when payment is absent.

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%, so the baseline is 3, but the description adds value the schema cannot: it maps which query parameters belong to which route (lat*/lon* for /nearby, q/country/kind/offset for /search, min_population/sort for /countries), plus the star marking required lat/lon. The schema only describes `params` as a generic string map, so this routing detail is genuinely additive. It omits value formats and allowed values for kind/sort.

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 a specific resource ('World Markets: Farmers, Flea, Night and Fish Markets') and an explicit verb-plus-outcome ('Find real-world markets anywhere'), so an agent knows exactly what domain this covers. It never names a sibling tool, but the resource is distinctive enough in the list (airports, colors, exchanges, etc.) that confusion is unlikely.

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?

Enumerates the five routes with the parameters each accepts, which effectively tells the agent which entry point fits 'look up by id', 'browse kinds', 'find nearby', 'text search', or 'browse by country'. It also states the cost and the free-preview escape hatch, which is real decision-relevant guidance. It stops short of explicit when-not or alternative-tool routing.

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