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

Annotations already declare readOnly/idempotent/non-destructive, so the description adds genuinely new behavioral context: the tool does not itself pay, it returns a URL, and payment must happen through an external x402 client via USDC on Base. This is exactly the kind of side-effect disclosure annotations cannot convey.

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 sentences, front-loaded with the core purpose and price/purchase model. The kind enumeration is dense but every item earns its place by disambiguating the enum; no filler text.

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 and does so: it states the returned URL leads to an HTTP 402 with the exact price. Combined with the kind coverage, an agent has enough to call and complete the flow correctly.

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 50% – id is documented in the schema, but kind is a bare 9-value enum. The description compensates by defining each kind (liveness, paygraph, drain, incidents, peer, bundle, reval, statement, counterparty) and noting the id semantics for counterparty (a receiving 0x address).

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 gives a specific verb+resource ("Price and how to buy a dated evidence pack over x402") and enumerates the 9 kinds it can quote. It is clearly distinguishable from most siblings, though it does not explain why an agent would pick this over the overlapping agent_statement or counterparty_preview tools.

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 explains the downstream workflow (an x402-capable client fetches the returned URL, receives HTTP 402, retries with a signed payment), which is useful operational guidance. However, it gives no explicit when-to-use or when-not-to-use guidance relative to the sibling tools that surface similar data.

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