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

Annotations already cover readOnly/idempotent/non-destructive, yet the description adds real behavior beyond them: only the caller's own receipt is accessible, foreign and nonexistent order numbers are indistinguishable (same 404, an anti-enumeration property), and card token/BIN are withheld from output. These are meaningful disclosures an agent could not infer from annotations.

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 returned fields, and the important scoping/404 caveat follows quickly. The trailing bilingual keyword list ('EN: credit, receipt, invoice...') is retrieval padding that dilutes an otherwise tight description.

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 single-parameter read tool with no output schema, the description supplies the returned-field list, the error semantics, the data-redaction guarantee, and where to source the ID — everything needed to call it correctly, with annotations covering safety.

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 schema already explains that order_id is the chargeup:sumup row from onto_credit_balance. The description restates this same origin, adding little new syntax or format 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 ('Beleg ... lesen') and enumerates exactly what the receipt contains (Bestellnummer, Datum, Betrag, Credits, Status, Transaktion, Zahlungsdaten). This clearly separates it from onto_credit_balance (balance), onto_credit_chargeup (top-up), and onto_credit_checkout.

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?

Tells the agent where to obtain the required order_id ('Die Bestellnummer steht in onto_credit_balance'), which is actionable routing to a sibling. It also clarifies that foreign/nonexistent IDs yield the same 404, but it does not explicitly name which sibling to use for other receipt-adjacent needs (e.g. balance vs. chargeup).

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