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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds that retrieval is restricted to issued invoices and that the XML can be ZUGFeRD/Factur-X or XRechnung, which is useful context, but it omits what happens if the document has no e-invoice attached or whether the returned text is raw XML or transformed.

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?

One short, front-loaded sentence with no filler. The trade-off is that it is a verbless noun phrase, so the key action has to be read off the tool name.

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 two-parameter read tool with no output schema, the description covers the resource and the return medium but leaves the enum parameter's effect and the failure case (no e-invoice present) unexplained. It is minimally viable rather than complete.

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 50% and `profile` has no schema description beyond its enum. The description mentions both formats but never says that `profile` selects among them, nor what the default is when omitted — leaving a genuine ambiguity about whether the parameter filters or converts. It adds almost nothing beyond the schema.

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?

The description names a specific resource (the e-invoice XML of an issued invoice) and enumerates the supported format families (ZUGFeRD/Factur-X, XRechnung), plus the returned medium ("als Text"). That differentiates it from the sibling download_document_pdf, though the verb itself only lives in the tool name.

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?

There is no explicit when-to-use guidance: nothing tells the agent to prefer download_document_pdf for the PDF rendering, when an e-invoice actually exists, or when the `profile` argument should be supplied. The only usage signal is the implicit scope constraint "einer ausgestellten Rechnung", which the agent must infer.

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