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

With no annotations, the description carries the full burden; it does add genuinely useful behavioral context — 'official KoSIT', signed Ed25519 VCs, and 'zero retention' — which a caller could not infer from the schema. However, it omits what happens on invalid input (error vs. validation result), that a fee may be charged (implied by max_accepted_fee_eur), and the shape of the issued VC.

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 compact sentences, front-loaded with the core capability. It is efficient with little waste, though the density of jargon (KoSIT, VCs) and absence of any clarifying clause makes it slightly abrupt for a tool with three parameters.

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 validator that issues signed credentials with no output schema and no annotations, the description is under-specified: it does not explain the return value (the VC), invalid-input behavior, fee mechanics, or the mandate parameter. An agent cannot confidently invoke or interpret results from this text alone.

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%: xml_content is described, but max_accepted_fee_eur (with a default) and ap2_intent_mandate_id are undocumented in both schema and description. Because coverage is below 50%, the description is expected to compensate, yet it explains none of the parameters and never mentions the fee/mandate semantics.

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 ('validator' / validating) and resource ('EN 16931 & XRechnung XML'), so an agent knows exactly what it acts on. The domain is clearly distinct from the siblings (redaction, sanctions/KYB screening), though the description never explicitly differentiates itself.

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 guidance on when to use this tool, when not to, or what alternative applies when the XML is not EN 16931/XRechnung. Usage is only inferable from the tool name; no prerequisites or exclusions are stated.

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