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

Annotations already indicate a non-readonly, non-idempotent, open-world operation. The description adds important behavioral context by stating that a payment process is triggered and that it should only be executed on explicit command. It does not detail failure modes or whether external payment confirmation is asynchronous, but it substantially improves safety awareness beyond the annotations.

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 compact and front-loads the action and the safety constraint. The trailing EN keyword list is useful for search but slightly less relevant to invocation, keeping it just below the top score.

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?

Given one required parameter, no output schema, and annotations covering safety traits, the description is largely complete: it explains the action, cautions execution, points to alternatives, and suggests balance checking for success. It could say more about what a successful checkout returns or whether follow-up confirmation is required, but the essential invocation context is present.

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%, and the single parameter 'credits' is already documented in the schema with its EUR conversion. The description does not add parameter-level meaning beyond what the schema provides, so the baseline score for high coverage 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 states a specific action and resource: purchasing credits via checkout, explicitly framed as starting a payment process. It also names sibling tools for related credit operations, so an agent can distinguish this from chargeup, prepaid creation, and balance checking without opening schemas.

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 gives an explicit execution condition: only run on explicit instruction. It also routes the agent to alternatives for direct top-up (onto_credit_chargeup) and prepaid quotas (onto_credit_create_prepaid), and points to onto_credit_balance for checking success.

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