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

With no annotations, the description carries the full burden and does substantial work: it discloses the x402 micropayment mechanism and exact cost ($0.05 USDC per call, _meta["x402/payment"]), the free 3-row sample escape hatch, the upstream source and license (WFP market price monitoring, HDX, CC BY-IGO), the monthly refresh cadence, and a scope disclaimer ("Facts, not trading advice"). It omits error behavior, rate limits, and any per-route row caps, which keeps it out of 5 territory.

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 single paragraph is front-loaded with the headline value proposition, then coverage, then return content, then routes, then pricing — a sensible information hierarchy with no filler sentences. It is dense rather than bloated, though the run-on route list packed with parenthetical parameters slightly hurts scannability.

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 tool with a nested open-ended params object, no output schema, and no annotations, the description covers the essentials: what the data is, what a result contains, which routes exist with their filters, what it costs, and how to get a free preview. The remaining gap is that an agent must still guess parameter value formats (e.g. commodity codes, country codes) and whether unpriced months or missing countries are silently dropped.

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, and the description mostly duplicates the route list already present in the route property's enum text. It does add marginal value by naming each route's accepted query parameters (/top takes commodity, min_ratio, limit; /persistent takes min_months) and flagging country as required with an asterisk. Since params is an open string map in the schema, this per-route parameter enumeration is the only real constraint signal available, but it is terse and gives no value formats or defaults.

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 opening clause defines the resource precisely — within-country price dispersion for the same commodity, with the concrete 2-50x magnitude and the covered universe (69 low- and middle-income countries, food/fuel/wages). It lists the exact facts returned (cheapest/dearest market, ratio, distance, persistence pairs), so an agent knows what it gets. It does not name or contrast the overlapping siblings (prices, local-markets, markets), which keeps it below a 5.

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?

Usage is conveyed indirectly through the route enumeration, which lets an agent infer that /top is for rankings, /country for a single place, /countries for coverage, and /persistent for recurring outliers. There is no explicit when-to-use versus sibling tools and no statement of when this tool is the wrong choice. The payment and sample hints are operational rather than selection guidance.

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