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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so 'Rein lesend' largely restates structured data. The description contributes the useful framing that this is a pre-flight check for a pay-per-use account, but discloses nothing about the returned balance format, currency, or freshness. With annotations carrying the safety profile, a 3 is appropriate.

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 instruction is front-loaded in the first three clauses with no waste. The trailing '| EN: credit, balance, pricing, billing, top-up, checkout' is keyword stuffing rather than descriptive content, which costs it the top score.

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 zero-parameter, read-only check with no output schema and rich annotations, the description covers everything an agent needs: what it returns conceptually, when to call it, and where to go for the related operations.

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 document and the baseline is 4. The description claims nothing about inputs, which is consistent with the empty schema.

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?

States a specific verb and resource ('das aktuelle Credit-Guthaben abrufen') and qualifies the account type (Pay-per-Use). It explicitly separates itself from three named siblings (onto_credit_pricing, onto_credit_chargeup, onto_credit_checkout), so an agent can pick it 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?

Gives an explicit when-to-use condition ('vor kostspieligen Aktionen pruefen, ob Guthaben vorhanden ist') and routes the agent to the correct alternatives: pricing for cost lookup, chargeup/checkout for topping up. Nothing is left to inference.

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