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

Annotations already cover readOnly/idempotent/destructive/openWorld, but the description adds material context beyond them: the free/no-gas/no-broadcast economics, the fact that no on-chain side effect occurs, and the shape of the failure signal ('Returns isValid plus invalidReason when the payload cannot clear'). It stops short of describing rate limits or auth requirements, so a 4 rather than 5.

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?

Five short sentences, front-loaded with the action and endpoint, then the checks performed, the cost/side-effect profile, and the response shape. There is no filler and every clause carries distinct 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 forwarding tool with an output schema present, the description supplies what the structured fields do not: the upstream endpoint, the recovery/validation steps, the absence of broadcast, and the availability of invalidReason. Nothing an agent needs to invoke it correctly is missing.

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% and the nested body schema is thoroughly documented (signer, payee, USDC atomic units, versioned field names), so the schema does the heavy lifting. The description only adds that the JSON body is forwarded verbatim, which is a small contribution over the baseline of 3.

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 a specific verb (forward/verify) and resource (x402 payment envelope), and the accompanying behaviors 'No broadcast', 'No gas', and 'only forwards the JSON body' make it unmistakable that this tool does not settle funds. An agent can distinguish it from x402_facilitator_settle purely from behavior, 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?

The description makes the dry-run nature of the tool clear via 'No gas. No broadcast.' and 'authorization still lives in the existing facilitator implementation', which implies when this is appropriate versus an actual settlement. It does not, however, explicitly name x402_facilitator_settle as the alternative for moving funds, so the routing guidance is inferred rather than stated.

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