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

Beyond the destructiveHint and readOnlyHint annotations, the description discloses that money settles from the agent's own wallet, that a two-step x402 payment flow is needed, and that idempotency_key prevents double payment—significant operational behaviors not captured in the schema.

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?

Four short sentences cover purpose, quote mode, payment flow, and idempotency guidance. Every sentence earns its place, and the most important action is front-loaded.

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 payment tool with no output schema, it explains the two-phase flow, the wallet implication, and retry behavior. It doesn't spell out the exact structure of the x402 response, but the description is sufficient to invoke both request phases 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 description coverage is 100%, so parameters are already documented. The description adds some workflow context around quote_only, payment_signature, and idempotency_key, but the marginal value over the schema is modest.

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 opens with 'Buy a service,' a specific verb and resource, and immediately distinguishes quote-only mode from actual payment. This clearly positions it against siblings like charge_refund, charge_get, and browse_catalog.

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 gives clear when-to-use guidance: 'Pass quote_only to get the price... without paying anything,' otherwise pay, and it instructs on idempotency_key for retries. It does not explicitly name alternative tools, but the workflow conditions are clear.

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