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

With no annotations, the description carries the full burden, and it does disclose two meaningful traits: it issues signed Ed25519 verifiable credentials and has zero data retention. However, it omits key behavior for a paid mutation-like call: what happens on invalid XML, whether a fee is charged on failure, and what the returned VC contains.

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?

Two short, front-loaded sentences with no filler; the validator identity comes first and the retention guarantee last. The telegraphic 'Zero retention.' fragment is slightly clipped but still informative rather than wasteful.

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 3-parameter tool with no output schema and no annotations, the description covers identity and privacy but not the paid-call mechanics, failure behavior, or the shape of the issued credential. An agent would still be guessing about cost-on-failure and output format before invoking it.

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 67%, and the description adds no meaning for any parameter. The fee cap and the undocumented ap2_intent_mandate_id are left entirely to the schema, and the description never explains the payment/mandate model that those parameters imply.

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 verb and resource ('EN 16931 & XRechnung XML validator') and adds distinguishing traits (official KoSIT, signed Ed25519 VCs, zero retention) that clearly separate it from the PII-redaction and sanctions-screening siblings. It stops short of 5 because the VC/Ed25519 phrasing is jargon-heavy and the core action is compressed into a noun phrase rather than a clean verb statement.

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 or when-not-to-use guidance, and no mention of alternatives or prerequisites. An agent can infer that this is for validating e-invoice XML, but nothing tells it when to prefer this over other validation paths or what input conditions are required.

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