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

With no annotations, the description carries the behavioral disclosure burden and does so well: it states that the tool returns a payment URL and a PENDING API key that activates automatically after payment clears. It does not cover edge cases like repeated checkouts or failed payments, but the core transaction flow is transparent.

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 two compact, front-loaded sentences: the first states the action and purpose, and the second explains the return values and activation behavior. There is no filler, redundancy, or unnecessary restating of schema fields.

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 3-parameter tool with full schema coverage and an output schema, the description covers the purchase flow, return contract, and post-payment activation. A more explicit reference to securityscan_pricing for users only checking prices would make it fully complete.

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 documents tier, email, and existing_key. The description adds no parameter-level meaning beyond what the schema provides, so the baseline score of 3 is appropriate.

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 opens with a specific verb and object: 'Start a Stripe checkout to buy a SecurityScan tier' and clearly frames this as agent-native sales. It is easily distinguished from sibling scanning/audit tools because it is the only one focused on checkout and purchase.

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 clearly implies the trigger context: use this when the user wants to buy or upgrade a SecurityScan tier, and it emphasizes 'no other setup step.' It does not explicitly name securityscan_pricing as the alternative for pricing-only questions, so it stops short of full routing guidance.

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