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

Adds real value beyond the annotations: it states that actual money moves / a payment is triggered, and warns that the amount is a payment rather than a refund. That is consistent with openWorldHint=true and destructiveHint=false and reinforces the billing-risk profile. It stops short of describing what happens to an invalid code or whether failures leave partial state.

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 warning and the purpose are front-loaded, followed by alternatives and next state in a logical order. The trailing "| EN: credit, balance, pricing, billing, top-up, checkout" tag block is keyword padding rather than actionable information.

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 money-movement risk, gating condition, alternatives, and follow-up tool are all covered, which is the important part for a non-idempotent billing mutation. But with required=[] and two distinct modes, the agent is left without guidance on which parameter to supply in which situation, a meaningful gap for this tool.

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% and each parameter is already documented (admin-only credits, agent self-service prepaid code), so the baseline is 3. The description only adds the clarification that the amount is a payment, not a refund. It never explains how the two parameters select different modes or that neither is required.

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?

"Credits aufladen (Guthaben erhoehen)" gives a concrete verb and resource that reconcile the ambiguous name/title pair (chargeup vs. Redeem Prepaid Code). It names sibling payment tools, so the agent can place it in the billing family. It does not, however, distinguish the two operating modes implied by the parameters (manual admin top-up vs. prepaid code redemption).

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?

Explicit gating: "nutze es nur auf ausdrueckliche Ansage" tells the agent this requires user instruction before invocation. It also names the alternative paths (onto_credit_checkout, onto_credit_create_prepaid) and the follow-up tool (onto_credit_balance), which is exactly the routing information needed.

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