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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world. The description adds meaningful safety context beyond that: it never performs or initiates a payment and collects no payment data, which is exactly the compliance concern for a payment-link tool. It also clarifies what the return actually is (a link vs an order page).

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 short sentences, front-loaded with the core purpose, then the variant semantics, then the safety caveat. No filler.

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 appropriately explains the return (secure page/link) per payment method and covers the critical safety posture. It stops short of specifying URL format or whether the link expires, but it is complete enough for correct invocation.

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 100%, so the baseline is 3, but the description adds real semantic value for payment_method by explaining that card returns a Stripe Checkout link while mobile_money returns an order page containing the Mobile Money form. That goes beyond the schema's terse 'card (Stripe) or mobile_money'.

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: returns the secure page where the customer pays for an ISBN pack. It distinguishes the two return variants (Stripe Checkout link vs Mobile Money order page). It does not explicitly differentiate from the sibling tools, so it falls 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?

Usage is implied by describing the payment-method variants (card vs mobile_money), but there is no explicit statement of when to call this instead of get_isbn_offer or get_required_book_info, nor any prerequisites. Adequate but leaves routing to inference.

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