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

Adds real context beyond annotations: the operation is non-charging, the quote has a 15-minute TTL, and the agent must ask the user to confirm before paying. It does not discuss retry/idempotency behavior even though the schema carries an idempotencyKey, which is the one behavioral detail left implicit.

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 purpose, then precondition, then next actions, then expiry. Every sentence carries information, though the payment-path sentence mixes two distinct flows and could be tighter.

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 should indicate what a quote returns (amount, currency, quote identifier, paymentUrl for x402); it only alludes to a paymentUrl in passing. For a stateful, address-dependent quoting tool this leaves the agent guessing about the response shape.

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% across 6 parameters including a nested address object, so the description must carry the load. It only clarifies that the shipping address must be complete; it says nothing about bookToken (a 64-char hex token), idempotencyKey (the 8+ char retry key), quantity bounds, or the 2-letter country format — the most opaque inputs go unexplained.

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 ('Prepare a fixed payment quote for a printed book') plus the scope of what the quote covers (shipping, MPP, x402/USDC on Base). It explicitly contrasts with the sibling pay_book ('No charge yet... pay_book for MPP'), so an agent can tell quoting apart from paying without inspecting either 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?

Gives a concrete precondition ('Requires a complete delivery address') and a clear next-step routing rule ('pay_book for MPP, or POST paymentUrl with an x402 client for USDC'). It does not address when to prefer this over the sibling create_checkout, so a small ambiguity about the alternative entry path remains.

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