Get a checkout link for a paid plan

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

Beyond the annotations, it discloses that no charge happens until the owner pays, that the plan activates within a minute, that an API key is required, and that an existing subscription yields 409. This adds meaningful behavioral context without contradicting the structured 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 front-loaded with the core action, then efficiently covers usage triggers, prerequisites, plan details, and behavioral caveats. Every sentence contributes distinct, decision-relevant information; there is 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?

For a one-parameter tool with no output schema, the description covers the essential context: when to call it, what it returns (a checkout link), authentication needs, plan semantics, payment timing, and the error case for existing subscriptions. An agent has what it needs to select and invoke the tool correctly.

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?

The single plan parameter is already enumerated in the schema, but the description adds real business meaning: payg is per-check with no monthly fee, solo and firm are monthly, and firm includes more keys. It also points to current pricing, going well beyond the schema's bare enum.

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 states a specific verb and resource: "Get a Stripe Checkout link that upgrades this API key's account to a paid plan," and even includes the endpoint. It clearly distinguishes this billing tool from the sibling checking/reporting tools like check_citations and coverage.

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 explicit triggers: use it when a check returns 402 or 429, or when the user asks to upgrade. It also explains when not to use it: an account with an existing subscription returns 409 and should use the billing portal instead.

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