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

With no annotations provided, the description carries the behavioral burden and does well: it discloses that the operation is a 'Light read' and quantifies the cost at 0.2 credit, which is real operational context beyond the name. It stops short of covering response shape, caching, or rate limits, but the read-nature and cost are the essentials.

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 that front-loads what is returned, then closes with the cost note. Every clause carries information, including the useful enumeration of deliberate non-goals such as Peppol transmission and French accredited-platform duties.

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, no annotations, and no parameters, the description must convey what the agent gets back, and it does: rules checked, syntaxes read/produced, and explicit exclusions. Nothing an agent needs to decide whether to call it is missing.

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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; the baseline of 4 applies. The description correctly spends no words on arguments.

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 and resource: it returns the EN 16931 rules checked, the syntaxes supported, and the deliberate non-goals. This is clearly distinguishable from sibling action tools like validate_invoice and generate_invoice, so an agent can identify it as a capability-discovery read without opening the schema.

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 rather than stated: the description positions it as a read-only capability lookup, which an agent can infer is useful before validating or generating. It never explicitly says when to call this versus, say, get_usage, nor does it name any exclusion criteria.

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