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

With no annotations, the description carries the full burden and does well: it discloses that totals and the VAT breakdown are computed automatically, that the document is validated before being returned, and the cost (1 credit). The main gap is what happens on validation failure (error shape, whether partial data is returned).

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?

Three sentences, zero filler, front-loaded with what the tool produces, then the choice, then the guarantee. Even the credit-cost sentence earns its place as an operational constraint.

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?

No output schema exists, so the description usefully states the return artifact (validated UBL 2.1 XML) and the profile stamp. Complex nested input is fully covered by the schema. What remains thin is failure behavior and whether the produced XML is retrievable/stored after generation.

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%, so the baseline is 3, but the description adds value: it expands the terse enum values ('en16931', 'peppol') into their real specification names and explains the semantic model, and it frames the nested invoice payload as 'invoice data' that gets totals computed. It adds meaning beyond the raw enum.

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 precise verb+resource+output artifact: turns invoice data into a compliant UBL 2.1 XML document following EN 16931. The profile choice (EN 16931 vs Peppol BIS Billing 3.0) lets an agent distinguish it from sibling validate_invoice and extract_invoice without opening schemas.

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 a real decision point for the profile parameter ('Choose the plain EN 16931 profile or the Peppol BIS Billing 3.0 customization'), which is usable guidance. However it never says when to reach for this tool instead of validate_invoice or extract_invoice, and gives no prerequisites or when-not-to-use conditions.

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