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

Beyond the sparse annotations (readOnlyHint=false, destructiveHint=false), the description reveals the return value ('Returns a checkout_url'), the side effect ('the upgrade lands automatically once payment succeeds'), the auth requirement ('Requires the 'act' scope'), and scope binding ('always bound to your own enrollment'). This gives the agent a thorough behavioral model.

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 sentences, front-loaded with the primary action, and every clause adds necessary information: the thing created, the output URL, the post-payment effect, free-trial availability, auth scope, and self-binding. No filler or redundancy.

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 zero-parameter tool with no output schema, the description covers everything an agent needs: what it does, what it returns, what happens after payment, when it is available, and what permissions/scope apply. It is a complete operational specification for this use case.

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?

There are zero parameters, so the schema leaves nothing to document. The description adds semantic value by explaining the implicit context ('THIS product run', 'bound to your own enrollment'), which tells the agent why no parameters are needed and how the tool is scoped. Baseline 4 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 resource: 'Create a Founder-tier checkout link for THIS product run.' It clearly distinguishes itself from siblings like create_topup by explicitly naming the output (checkout_url) and the purpose (unlocking Founder-only growth controls).

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 provides clear context: 'Reachable on a free trial because it is the path TO Founder' tells when to use this tool. It doesn't explicitly exclude alternatives among the siblings (e.g., create_topup), but the context makes the intended use unambiguous.

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