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

The annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds context the annotations do not: this is a paid endpoint and the response carries the exact x402 v2 payment requirements and the query parameters a subsequent paid request needs, which is the key behavioral fact an agent must know.

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?

A single front-loaded sentence that leads with the resource and then the contents; the 'check (one payment, one check)' parenthetical is slightly cryptic, but there is no filler and the actionable instruction sits at the end where it is easy to catch.

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 must convey what comes back, and it does: product list, prices, required request parameters, and payment requirements. For a zero-parameter read tool this is essentially complete, though it doesn't cover ordering, filtering, or how many products are returned.

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?

The tool takes zero parameters, so the baseline is 4. The description's mention of 'the query parameters the paid request needs' describes the return payload rather than inputs, and doesn't confuse the no-argument signature.

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 names the resource ('every product for sale') and enumerates what comes back with each entry: price, required query parameters, and x402 payment requirements. The verb is implicit (a listing/get rather than an explicit action verb), but the scope is concrete enough to distinguish it from get_docs, get_service_status, and lookup_site.

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?

It gives an explicit trigger — 'Call this before buying' — which tells the agent exactly when this tool is the right one. It doesn't name alternatives or exclusions, but no sibling covers product/pricing discovery, so nothing is left ambiguous.

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