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

Annotations declare readOnlyHint=false and openWorldHint=true; the description adds real context beyond them by disclosing the authorization requirement, the human-in-the-loop payment flow, and that no charge occurs at call time. It stops short of stating whether repeated calls create multiple concurrent checkout sessions or how long a session 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?

Three short sentences that front-load the action and return value, then the payment-safety caveat, then the authorization constraint. No filler or repetition.

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 an output schema present and full parameter coverage, the description does not need to explain return values, and it covers the key concerns for a billing mutation: permissions and deferred charge. Minor gaps remain around idempotency and session lifetime, which an agent might want before calling twice.

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% and the enum's own description already explains pricing, $0.05 credits, and bonus tiers. The description only adds that exactly one pack is selected per call, so the schema is doing the heavy lifting, which lands at the baseline 3.

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 uses a concrete verb+resource pair ('Start a Stripe Checkout for one prepaid credit pack') and names the caller scope (the caller's organization) plus what it returns (the checkout page to open). This clearly separates it from siblings like get_credits, open_billing_portal, and request_payout_account_setup.

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 the essential gating context: only organization owners and admins may call it, a credential is needed, and nothing is charged until payment happens on the returned page. It does not explicitly contrast with open_billing_portal or get_credits, so the when-to-use-vs-alternative link is left implicit.

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