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

Annotations already cover readOnlyHint, idempotentHint, openWorldHint, and destructiveHint, so the bar is lower. The description adds useful context beyond those: the data source is the free EU VIES register, scope includes any EU member state and Belgian KBO/BCE, and the returned fields are name, VAT id, address, and status. It does not discuss failure modes or rate limits, but the added context is meaningful.

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?

The description is two sentences with no filler. The first sentence front-loads the action, resource, and source; the second covers return values, read-only status, and workflow pairing. Every clause earns its place.

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?

This is a simple two-parameter, read-only lookup with no output schema, and the description is complete for invocation: it states the source, scope, returned fields, and a concrete use case. It also compensates for the missing output schema by naming exactly what the caller gets back.

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 description coverage is 100%: both vatNumber and countryCode already have detailed descriptions, including examples and default behavior. The prose mostly restates 'VAT or enterprise number' without adding new parameter semantics, so the baseline score of 3 is appropriate.

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: 'Look up an official European company by VAT or enterprise number' via the EU VIES register, and it lists the returned fields. It is clear, but it does not explicitly differentiate itself from nearby siblings like lookup_peppol_participant or analyze_kbo_financials; it only mentions a pairing with format_peppol_invoice.

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?

The description gives a concrete workflow signal, 'pairs with format_peppol_invoice to resolve a buyer,' and notes it is read-only, which helps an agent decide when to call it. It does not explicitly state when not to use it or name alternative tools, so it stops short of full routing guidance.

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