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

Adds substantial behavior beyond the annotations: it debits the billing.addon.hook add-on, buys a 30-day window, never re-serves the signing secret, checks the URL at registration (refusing loopback/private/metadata hosts), returns a payment_required challenge when unpaid, and refunds on refusal. This aligns with (and enriches) idempotentHint=true and openWorldHint=true rather than contradicting them.

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?

The core purpose is front-loaded, but the text repeats verbatim phrases — 'x402 exact USDC Base' and 'After paying, poll /v1/resolutions/:id until horizon_end' both appear twice — and the payment rail details are dense. It is informative but wastes space on duplication.

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 an output schema present (so return values need no explanation) and only two params, the description covers payment, registration semantics, secret handling, and URL validation. It is close to complete for a paid write tool, with only minor gaps in post-registration expectations.

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 0%, so the description must carry the load, and it largely does: `payer` is framed as a Base address 0x… with three accepted delivery channels (tool argument, x-tollbridge-payer header, PAYMENT-SIGNATURE), and `url` as a public http(s) URL validated at registration. That is meaningful semantics absent from the schema.

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?

Names a specific verb+resource: 'register an outcome hook endpoint: a public http(s) URL that Tollbridge POSTs to when one of the payer's decisions settles'. This is unambiguous and clearly distinct from every sibling (leaderboards, blotter, risk, etc.), none of which manage webhooks.

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?

Gives clear operational context: register after paying, then poll /v1/resolutions/:id until horizon_end, and notes that re-registering the same URL inside its window replays without a second charge. It lacks explicit 'do not use this when…' guidance, but no sibling competes for this function, so the routing need is low.

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