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

Annotations already flag a non-read-only, open-world, non-idempotent mutation, and the description adds genuinely new behavior: the link is created in Stripe, the agent must not complete payment, the saved card is pre-filled, and the response carries checkout_url/session_id. It stops short of warning that repeated calls create separate links (relevant given idempotentHint=false).

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 dense sentences ordered as action, constraint, follow-up, with the verb and price tiers front-loaded. Every clause carries operational information; nothing is redundant padding.

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?

With only one enum parameter and no output schema, the description must cover the return value and hand-off, and it does: checkout_url plus session_id and the check_payment follow-up. Nothing an agent needs to call this 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 100% with an enum for credits, so the baseline is 3; the description earns above that by mapping each enum value to a concrete price (10/R$80, 30/R$200, 80/R$500), which is business meaning the schema does not contain.

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 concrete verb+resource ('Cria um link de pagamento do Stripe') and immediately scopes it to buying a credit package, including the exact price tiers. An agent can distinguish this from siblings like check_payment or account without opening any 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?

It prescribes the full workflow: ask the user which package first, do not pay yourself but hand the checkout_url to the user, then call check_payment with the session_id. Both the precondition and the explicit next-tool routing are stated, leaving nothing to inference.

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