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

Beyond the annotations, the description discloses important behavioral details: the URL leads to a one-time card-entry flow, the plan switches immediately after payment, and the billing basis is monthly pre-tax with metered overage. It also notes the api_key requirement. Nothing contradicts the annotations.

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?

The description is compact and front-loaded with the core return value, followed by the workflow and pricing context. Each sentence earns its place, though it is slightly denser than strictly necessary for a two-parameter tool.

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 simple two-parameter tool with no output schema, the description covers the return value (Checkout URL), the required authentication, the effect, and the pricing model. It is complete enough for correct invocation, though it doesn't mention URL expiration or repeated-call behavior, which would be nice but not essential.

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 explains both parameters. The description does add useful context by listing the plan values and noting that the api_key comes from signup, but it doesn't fundamentally expand on the schema's parameter meanings.

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 clearly states a specific action and resource: it returns a Stripe Checkout URL for paid plans (starter/standard/business). It also explains the intended outcome. However, it doesn't explicitly contrast itself with sibling tools like get_billing_portal, so it lacks explicit sibling differentiation.

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?

The description gives a clear use context: the user opens the returned URL and enters card details, and the plan switches immediately with only this one human step. This is enough to understand when to use it, but it does not explicitly state when not to use it or mention alternatives like get_billing_portal.

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