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

Annotations already declare readOnlyHint=false, openWorldHint=true and idempotentHint=false, so the bar is lower. The description still adds valuable context beyond them: it moves real money / triggers a payment, requires explicit instruction, and clarifies the amount is a payment not a refund. It does not describe failure/retry behavior, which keeps it from a 5.

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 about real-money movement and the sibling alternatives are front-loaded and each sentence earns its place. The trailing keyword block ('| EN: credit, balance, pricing, billing, top-up, checkout') is search fodder rather than agent-facing content and slightly dilutes the otherwise tight 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?

For a money-moving tool with no output schema, the description covers the critical dimensions: what it does, the danger profile, the required precondition, the alternatives, and the follow-up tool for verifying the new balance. Nothing needed to call it correctly is missing.

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%, so the schema already documents both parameters (credits = admin manual top-up, prepaid_code = agent self-service), making 3 the baseline. The description adds directional meaning not in the schema by clarifying the amount is an outbound payment rather than a refund, and by flagging that prepaid/checkout are alternative paths.

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 verb and resource ('Credits aufladen / Guthaben erhoehen') and explicitly names the sibling alternatives (onto_credit_checkout, onto_credit_create_prepaid). An agent can distinguish this from other credit tools without opening any schema.

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 when-to-use constraint ('nutze es nur auf ausdrueckliche Ansage') and names two alternative payment routes by tool name, plus the follow-up state check (onto_credit_balance). This is exactly the routing guidance an agent needs.

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