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

Annotations already provide readOnlyHint=true and destructiveHint=false. The description adds key behavioral context: 'Full report, never fails fast' and clarifies that validation does not imply legal/fiscal/compliance guarantees. This goes beyond annotations and aligns with them.

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 sentences, no redundancy. The first sentence immediately states purpose and scope, the second clarifies limitations. Every word adds value.

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?

Given the tool has 1 required parameter, nested object, and output schema exists, the description is complete. It explains what is validated, what is not, and the nature of the output (machine-readable issues, never fails fast). No gaps.

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 100% with a single parameter 'invoice' described as 'The invoice payload to check.' The description adds meaning by enumerating what is validated (schema problems, VAT-id format, date sanity, BIS 3.0 completeness, computed totals), which helps the agent understand the tool's scope beyond the schema.

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 clearly states the tool validates EU invoice structure and reports machine-readable issues, with specific examples (schema, VAT format, date sanity, BIS 3.0 completeness, computed totals). It distinguishes from siblings by explicitly stating what it is not (legal approval, sending Peppol).

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 explicitly states when to use (structural validation) and when not (not for legal/compliance, never sends). It also provides exclusion conditions ('never sends a Peppol invoice, gives no legal guarantee'), which helps the agent decide against sibling tools.

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