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

Annotations already declare the mutation, open-world, and idempotency profile; the description adds the important clarification that this creates payment instructions rather than moving money, plus the retry instruction to reuse idempotencyKey. It stops short of describing required auth scopes or what happens to a duplicate key with a different payload.

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 action and chain choices, with no filler. The product/pricing sentence is dense but every clause carries decision-relevant 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 an open-world payment-creation mutation with no output schema, the description never says what comes back (checkout URL, invoice address, payment id) or how the agent should poll afterward via check_payment. The alias ambiguity between chain and method is also unaddressed.

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 only 43%, and the description compensates by explaining the economics of amountCents ($1 = 10,000 standard sends), the $1/30-days hosting rate, and the domainId requirement for domain_addon. It does not address the chain-versus-method legacy alias relationship, which is the one genuinely confusing parameter interaction.

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 ('create a card checkout or native USDC invoice') and enumerates the supported chains and purchasable products (mail_credits, domain_hosting, domain_addon). An agent can distinguish this from check_payment or check_sending_status 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?

Gives clear selection guidance between the three product kinds, including the rule that domain_addon is for a second verified domain under active primary hosting, and states the 'with your operator's authorization' prerequisite. It does not explicitly point to check_payment as the follow-up, so it falls short of full alternative routing.

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