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

Annotations already declare the non-destructive, non-idempotent, closed-world mutation profile. The description adds real value beyond that: returns a 24-hour download URL plus computed totals, and is validated against the EN 16931 schematron in CI. It doesn't mention auth/quota beyond what the schema's api_key already covers.

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 dense sentences, front-loaded with what it produces, followed by the delta vs the sibling and the return value. No filler; every clause carries information.

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?

Covers output shape (download URL + totals), the profile enum context is handled in the schema, and key conditional requirements are stated. With nested objects and no output schema, a bit more on party/address requirements would make it fully complete, but it is sufficient to call correctly.

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 coverage is only 33%, so the description must compensate and does: it names the newly required fields (countryCode, vatId when taxRate > 0) and the optional e-invoice fields (paymentIban, paymentReference, buyerReference), which are the semantically tricky additions over create_invoice_pdf. Many nested item/party fields remain undocumented in the description, keeping it from a 5.

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 (generate) and resource (EN 16931 e-invoice as CII XML), and distinguishes itself from sibling create_invoice_pdf by name. An agent can tell exactly which document format this produces versus the PDF sibling.

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?

Signals when to use it (France Factur-X / Germany XRechnung mandates) and anchors it to the sibling by saying it shares create_invoice_pdf's JSON shape with extra fields. Lacks an explicit 'use create_invoice_pdf when you don't need e-invoicing' exclusion, so not full marks.

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