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

Beyond annotations (readOnlyHint false), the description discloses the return format variants ({checkoutUrl...} vs {transactionId...}), the directCharge flag behavior, and the authorization requirement (owner-only, billing scope). This is substantial behavioral context that annotations do not provide.

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 three concise sentences, each serving a distinct role: stating the action, specifying the parameter source, and describing return values and authorization. No unnecessary words.

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 the single parameter and absence of an output schema, the description fully covers the purpose, parameter origin, return variants, and authorization context. It provides everything needed to invoke the tool successfully.

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?

The input schema already provides 100% coverage of eurCents, including 'matching a pack returned by list_credit_packs.' The description restates the same information without adding new semantic detail, so the baseline of 3 applies.

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 explicitly states 'Begin a credit-pack top-up for the project owner' with a specific verb and resource. It clearly distinguishes from sibling tools by referencing list_credit_packs as the source of eurCents.

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?

The description tells the agent to pass eurCents from list_credit_packs and notes the owner-only billing scope requirement. This gives clear context for when to use, though it does not explicitly state when not to use or name alternatives.

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