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

Annotations already declare non-readOnly, idempotent, non-destructive, so the description correctly focuses on what annotations can't express: that this only mints a link and no money moves until the user confirms at Stripe, and the retry-key discipline. It doesn't say whether an existing checkout link is invalidated or how long a prepared link stays valid.

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, front-loaded with the core action, then the safety guarantee, then ordering, then retry guidance. No filler and no repetition of schema constraints.

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 5-parameter, no-output-schema mutation it covers the crucial 'no charge yet' semantics but leaves gaps: what the call returns (a URL? a session id?), how quantity affects the request, and what happens to a previously prepared checkout. An agent could call it, but would not know what to do with the result.

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%, so the description must carry the burden, and it only partially does: it explains bookToken's provenance (post email claim), country's meaning (destination, collected first), and idempotencyKey's retry role. bookId and quantity get no mention at all, leaving two of five parameters inferred purely from names and constraints.

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 action (prepare a Stripe checkout link) and the resource it depends on (bookToken minted after email claim). It implicitly separates itself from pay_book by stressing 'no charge occurs until the user confirms payment at Stripe', but it never names that sibling explicitly, so differentiation requires inference.

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 real preconditions: call after the email claim, collect the destination country first, and reuse idempotencyKey on retry. It also labels the step as optional. It stops short of stating when to skip checkout in favour of pay_book or create_payment_quote, so it is clear context rather than full routing guidance.

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