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

With no annotations at all, the description carries the full burden. It usefully discloses that this is a real money-moving charge ('auto_fill' charges a card directly) and that auth is handled via an automatic x-api-key header, but it says nothing about idempotency, retry/double-charge risk, what happens on decline, or what the auto_fill path returns.

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 action, then the mode branching, then auth. Nothing is padded, though the trailing API-key sentence is somewhat auxiliary and could arguably be folded into the auth context more tightly.

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 9-parameter payment-mutation tool with no annotations and no output schema, the description covers mode selection and auth but omits what the auto_fill path returns (payment id, status) and any error or idempotency semantics. It is adequate to start a call but leaves real gaps around outcome handling.

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 the schema already documents every parameter, including the 'required for auto_fill' notes on card fields. The description restates the same conditional requirement without adding format, validation, or sequencing detail, so baseline 3 applies.

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 names a specific verb and resource ('Creates a payment for a booking via Airwallex'), which clearly separates it from read-side siblings like get_payment_status or get_booking. It doesn't explicitly name an alternative tool, so it stops short of a 5.

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 useful conditional guidance for the two payment_type modes (card details needed for 'auto_fill', a URL returned for 'payment_link'), which helps the agent pick a mode. However, it offers no guidance on when to call this versus get_payment_status, no prerequisites around booking state, and no exclusions or failure conditions.

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