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

Annotations only give generic hints (openWorld, not read-only, not idempotent). The description adds the traits that actually matter here: it is a non-custodial pass-through that never holds keys or funds, never settles, charges no fees, and forwards the payment unchanged. It also explains the 402 handshake, which an agent could not infer from the annotations.

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 dense sentences with no filler: the forward-and-return behavior, then the 402 branch, then the trust and eligibility guarantees. The most decision-relevant facts (pass-through, payment handling) are front-loaded before the non-custodial assurances.

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 well, explaining that the seller's response is passed through unchanged and that a 402 yields the seller's payment requirements verbatim. It also covers the auth model (your own wallet) and supported listings. Minor gaps remain around non-402 errors, timeouts, and the largely undocumented query/method/content_type parameters.

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 63%, so roughly a third of the eight parameters (query, method, content_type, endpoint) are documented only partially or not at all. The description does contextualize x_payment and payment_signature by tying them to the x402 v1/v2 payment retry, which adds value beyond the schema. However, the remaining parameters get no semantic help from the description, so this sits at the baseline for moderate coverage.

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 states a precise verb and resource: it forwards a request to the seller's x402 endpoint and returns the seller's response. It is immediately distinguishable from siblings like search_kits or get_kit, which resolve listing metadata rather than perform the call. The scope constraint (only links.call / buy=relay_x402 listings) further sharpens what this tool does.

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 procedural when-to-use: call, and if the seller answers 402, sign with your own wallet and call again with x_payment or payment_signature. It also states the eligibility condition (only relay_x402 listings). It stops short of naming an alternative sibling for unsupported listings or non-payment flows, so it is clear context without explicit alternatives.

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