Report whether a public item appears buyable with explicit blockers such as out-of-stock or unknown. This is a preflight only: it never signs in, buys, creates an order or guarantees checkout. Price: $0.003 USDC per successful call.
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | Public HTTP(S) URL to inspect, resolve, or compare. | |
| variant | No | Public identifiers value used to scope this lookup. | |
| quantity | No | Requested item quantity to validate against provider limits. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Adds behavior beyond the annotations: it discloses a per-call price ($0.003 USDC per successful call) and clarifies that it is a non-mutating preflight against the target, which offsets the non-obvious readOnlyHint=false. It does not describe latency, failure modes, or rate limits.
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?
Three short sentences, each earning its place: capability, scope boundary, and cost. The key constraint (preflight only) is front-loaded before the pricing note.
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?
With no output schema, the description carries the return-value burden and does so partially by naming possible blockers. Pricing and safety boundaries are covered; the shape of the returned report could be spelled out further.
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%, so url, variant, and quantity are already documented, including the quantity bounds. The description adds no syntax or format detail for variant (a free-form nested object), so baseline 3 applies.
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 verb and resource: report whether a public item is buyable, with named blocker signals (out-of-stock, unknown). It is distinguishable from most siblings, though it never explicitly contrasts itself with the closest sibling, commerce_availability.
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?
Explicitly frames the tool as a preflight and excludes what it will not do (sign in, buy, create an order, guarantee checkout), which tells the agent when this is and is not the right call. It stops short of naming the alternative tool to use when a real checkout or availability query is needed.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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