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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description goes further by disclosing the actual mechanics (recovers the EIP-712 signer, runs USDC's and the seller's checks) and the failure behavior, including naming the EIP-712 domain mismatch with a concrete Base Sepolia example. It stops short of stating whether a successful check returns anything or whether it ever forwards the payment.

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 dense sentence that front-loads the action and then the mechanism, with zero filler. It is packed tightly enough that the clause chain ('recovers…, runs…, and when the signature fails names…') takes a moment to parse, but nothing is wasted.

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 compensates by explaining the diagnostic output on signature failure, which is the most decision-relevant return for an agent. Combined with schemas that document both input modes and all five optional params, an agent has enough to invoke it, though the shape of a successful result is left unspecified.

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 all five parameters (network, signature, x_payment, requirements, authorization) are already documented, including the two mutually exclusive input modes. The description adds no parameter-level detail, so the 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 ('Check a signed x402 USDC payment') plus the precise moment it applies ('before submitting it'). An agent can immediately distinguish this pre-flight validator from the unrelated siblings (histor_check, tool_list_cost, warden_scan).

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?

The phrase 'before submitting it' clearly establishes the usage context: this is a pre-submission validation step, not the submission itself. It does not name an alternative tool or an explicit when-not condition, so it falls short of a 5.

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