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

Annotations already cover the safety profile (readOnlyHint=false, idempotentHint=false, openWorldHint=true), so the bar is lower, but the description still adds genuinely new behavioral context: this triggers a real external payment flow and must only be invoked on explicit user instruction, and success is verified via onto_credit_balance. It stops short of stating cost implications, failure/rollback behavior, or auth requirements.

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?

Front-loaded with the action and the safety constraint, then routing, then verification. The trailing EN keyword list is retrieval padding rather than agent-facing prose, which is a minor blemish on an otherwise tight two-to-three sentence block.

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 one-parameter, non-idempotent payment trigger with no output schema, the description covers the important gaps: that it is a real payment, that it needs explicit consent, and where to check the outcome (onto_credit_balance). Only deeper failure/permission semantics are absent.

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 description coverage is 100% and the single parameter already documents 'Anzahl Credits (1 Credit = 0,01 EUR)'. The description adds no format, range, or unit detail beyond the schema, so the baseline 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?

States a specific verb+resource ('Credits per Checkout erwerben', i.e. start a payment/checkout) and explicitly contrasts itself with two named siblings (onto_credit_chargeup for direct top-up, onto_credit_create_prepaid for prepaid contingents). An agent can distinguish this from the 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?

Gives an explicit when ('start a payment transaction'), an explicit when-not/guard ('nur auf ausdrueckliche Ansage ausfuehren' – only run on explicit user instruction), and names the alternative tools for adjacent needs. Routing and the confirmation prerequisite are both stated.

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