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

Annotations already declare readOnly, idempotent, closed-world and non-destructive behavior, so the safety profile is covered. The description still adds genuine business context the annotations cannot carry: flat users (billing_model=flat) incur no credits, and the conversion rate of 1 credit = 0.01 EUR, which the agent needs to interpret results.

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 core meaning is front-loaded in one sentence, followed by the flat-model exception and the EUR conversion, both of which earn their place. The trailing "| EN: credit, balance, pricing, billing, top-up, checkout" is keyword padding that adds no semantic value and slightly dilutes the structure.

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 no parameters, no output schema and full annotation coverage, the description supplies what is needed: what the tool reports, that output is per-operation credit costs, and the pricing semantics. What is missing is minor — it does not say whether the list is static or reflects the account's current plan.

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 tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. No parameter claims are made or needed.

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?

"Zeigt, wie viele Credits jede Operation verbraucht" names a specific verb (show) and resource (credit pricing per operation), which is clearly distinct from the sibling balance/chargeup/checkout tools. It does not explicitly name those siblings, so an agent must infer the distinction from the name alone.

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: the agent can infer this is the lookup tool for pricing information, and the flat-model note hints at when the answer is zero. There is no explicit statement of when to use this versus onto_credit_balance, onto_credit_checkout or onto_credit_receipt, all of which sit in the same domain.

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