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

Goes well past annotations by disclosing the billing model ($0.002 USDC per successful call, x402 via Base/Solana/Arc) and that failed calls are not charged, plus the network limitation blocking costco.com and the data source (public page schema.org). Annotations only say readOnly/openWorld; the cost and reachability facts are behavioral context the agent cannot infer elsewhere.

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?

Front-loaded with purpose, then scope limits, then output fields, then price — a sensible order with no filler. It is one dense paragraph and the payment clause is long enough that it slightly dilutes the operational core, but every sentence carries information.

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 single-parameter lookup with an output schema and readOnly annotation, nothing an agent needs is missing: inputs, return fields, geographic/network boundary, cost, and failure-charging behavior are all covered.

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 the derivation rule for the ID ('the number at the end of a costco.ca product URL') and reiterates the 1-5 limit, which helps an agent map user input to a valid argument. It does not clarify format tolerance for full URLs versus bare IDs beyond what the schema already states.

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?

Opens with a specific verb+resource+scope ('Costco Canada (costco.ca) product tracker') and enumerates exactly what is returned (name, SKU, CAD price, availability, rating, category path, image, URL). It also bounds the input cardinality and names the two things it is not (no keyword search, no costco.com), so an agent can distinguish it from every retail sibling without opening the schema.

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?

Explicit exclusions are stated: no keyword search and US costco.com is unreachable, which are the two most likely misuse paths. It also tells the agent how to obtain the identifiers (the number at the end of a product URL). It stops short of naming which sibling to use instead for keyword-based product search, so it is clear context without a full routing table.

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