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

Annotations declare readOnlyHint=true and openWorldHint=false, and the description reinforces this by clarifying 'This tool never charges anything by itself,' resolving the obvious ambiguity of a tool named 'buy'. It adds genuine behavioral context — payment happens in the user's browser and pages are credited to this key's account only after payment completes. It omits link expiry or failure handling, keeping it from a 5.

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, front-loaded with the return value, then the agent action, then the safety clarification. Nothing is redundant or wasted.

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 two-parameter, no-output-schema tool, the description covers what is returned (a link), who acts on it, and when the side effect lands. Only edge details like link expiry or what to do if the user abandons checkout are missing.

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 coverage is 100% and both parameters are enums with inline pricing detail, so the description adds no param-level meaning beyond the schema. Baseline 3 is appropriate since the schema carries the full burden.

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?

States a specific verb and resource ('Return a Stripe Checkout link for a page pack') and describes the resulting flow, which makes it unmistakable against siblings like check_balance or read_document.

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?

Explicitly instructs the agent what to do with the result ('Give the link to your user: they pay in their browser'), which is the key usage context. It lacks explicit when-not-to-use guidance or naming of alternatives, but the siblings are functionally distant enough that this is a minor gap.

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