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 value beyond that: it pins the spec version (v2.0.2), explains the two distinct checks performed, and lists what is returned (validity, parts, expected check digits). It omits auth/rate-limit detail, but for a read-only check that matters little.

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?

A single dense sentence, front-loaded with the verb and resource, and the return-value clause closes it efficiently. No padding, though the parenthetical BT-10 definition and spec version make it slightly heavy.

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?

With no output schema, the description usefully enumerates the return fields, and it defines the domain concept and spec version. The main gap is the unexplained lang parameter, which an agent cannot resolve from either structured or unstructured data.

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 50%: leitweg_id carries an example, but lang has only an enum and is undocumented in both schema and description. The description explains what leitweg_id represents (BT-10 buyer reference) but never mentions the lang parameter or its effect on output, so it does not compensate for the coverage gap.

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 (check) and resource (Leitweg-ID), defines what it is (buyer reference BT-10), and names the spec version and the two validation dimensions (format/check digit and Peppol registration). An agent can distinguish it from validate_einvoice and peppol_lookup 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?

Usage is implied: use it to validate a buyer reference and check Peppol registration. But there is no explicit guidance on when to prefer this over peppol_lookup (which likely also queries registration) or validate_einvoice, and no exclusions are stated.

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