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

Annotations declare non-readOnly, openWorld, non-idempotent, non-destructive; the description goes well beyond by clarifying this tool only produces links and performs no payment, that credits land immediately upon payment completion, and that user approval is required. This is exactly the mutation-adjacent context an agent needs.

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 front-loaded sentences with no filler; the link-only constraint and user-approval requirement are stated up front. Minor redundancy in repeating the 20-2000 range already in the schema.

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?

Even though an output schema exists, the description still characterizes the return values (checkout link, optional MPP URL), covers currency options, and spells out the safety boundary. Nothing needed to invoke it correctly is 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 already 100% for the single `credits` parameter, so baseline is 3; the description adds unit price ($0.50 each) and the 20-2000 range, giving useful cost context the schema lacks. It does not explain unit semantics further, so not a 5.

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+resource (returns payment links to buy credits) plus pricing, quantity range, and the two payment channels (Stripe checkout vs MPP purchase URL). An agent knows exactly what comes back without opening the schema.

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 says the tool cannot pay and that the user must be asked before calling and must approve before paying. Strong when-to-use and precondition guidance, though no sibling alternatives are named (none are comparable in this toolset).

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