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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description earns credit for disclosing that results come from the Peppol Directory (an external, potentially stale source) and enumerating precisely what each result contains, including conditional name/country fields "when published".

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?

Three sentences with zero waste: capability first, accepted inputs second, return shape third. Every sentence carries information an agent needs to select and call the tool correctly.

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 properly carries the return-value burden by listing registration status, BIS capability, and directory metadata. Slightly incomplete in that it doesn't say what a zero-match response looks like or whether multiple matches are common for VAT-based queries.

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 already 100%, setting a baseline of 3, but the description adds concrete format examples (0208:0123456749, BE0123456749, NL...B01) that clarify the accepted identifier shapes beyond the schema's bare enumeration. It does not specify normalization behavior for malformed IDs.

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 ("Check whether a company can receive e-invoices over Peppol") and immediately scopes it to participant lookup, which is clearly distinct from the sibling mutation/validation tools (create_einvoice, validate_einvoice, check_leitweg_id). An agent can identify the tool's job 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 — this is the pre-flight registration check before creating or validating an e-invoice — but the description never states when to use it versus check_leitweg_id or validate_einvoice, nor any prerequisites. The context is inferable from the sibling set rather than stated.

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