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

With no annotations, the description carries the full behavioral burden. It usefully discloses that this is a direct charge using raw card details and that the card data is not stored, but it omits key payment behavior such as whether the charge is irreversible, what authorization is required, and how idempotency is handled.

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 a single front-loaded sentence with no filler: the verb 'Charge' appears first, followed by the scope and the no-storage constraint. Every phrase carries information, even though the overall definition remains under-specified elsewhere.

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?

The output schema exists, so return values need not be explained. However, for a 12-parameter financial mutation with no annotations and 0% schema description coverage, the description is far too thin: it lacks parameter semantics, usage guidance, authorization expectations, and charge/idempotency behavior.

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 0% across 12 parameters, so the description must compensate but largely does not. 'Raw card details' loosely maps to card fields and 'current billing principal' hints at buyer identity, but it does not explain credits, required fields, defaults, payment_type, idempotency_key, or card_ssn/card_cvc semantics.

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 gives a specific action, 'Charge raw card details directly,' and scope, 'for the current billing principal,' plus a data-handling constraint, 'without storing them.' It is clear enough to distinguish a direct card charge from a stored-payment method flow, though it never explicitly says it purchases credits or names the sibling purchase_credits.

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?

Usage is only implied: 'raw card details directly' and 'without storing them' suggest this is for cases where card data is supplied directly rather than using a registered payment method. There is no explicit when-to-use, when-not-to-use, or named alternative such as purchase_credits or register_billing_payment_method.

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