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

Goes well beyond annotations: discloses that structured issues are returned instead of a file on rule violations, describes watermark and daily limit without subscription, specifies percentage calculation rules for allowances/charges, and details XRechnung output constraints (pure XML via REST API, required fields). This is rich behavioral context for a write operation.

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?

Dense but front-loaded with purpose, then structured into error handling, subscription limits, calculation rules, and XRechnung specifics. Every sentence carries useful information, though the length is substantial; for a complex tool this is justified and no major redundancy appears.

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?

Given the presence of an output schema, the description need not explain return values, but it still covers error returns (structured issues), rate limits, watermark behavior, calculation rules, and XRechnung requirements. An agent has enough information to invoke the tool correctly and interpret failure modes.

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?

With 100% schema description coverage the baseline is 3, but the description adds critical semantics: it explains how allowanceCharges amounts may be omitted when percent is set, gives the formula amount = round2(Menge × unitPriceNet × percent / 100), and clarifies that lineNetAmount, vatBreakdown and totals must be computed by the caller. It also names required XRechnung fields.

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?

Starts with a specific verb and resource: 'Erzeugt eine ZUGFeRD-PDF aus visueller PDF und strukturierten EN-16931-Daten (kein LLM).' This clearly distinguishes it from siblings like extract_invoice (extraction) and verify_zugferd (verification).

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?

Explains the retry workflow when EN-16931 business rules are violated, mentions extract_invoice as the correction counterpart, and gives conditional guidance (subscription status, profile='xrechnung' for public sector). It lacks explicit when-not-to-use or full alternative routing, but provides strong context.

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