validate_invoice_schema

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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is known. The description adds the return structure and a disclaimer about not being legal advice, which provides minor additional context.

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?

Description is brief, front-loaded with the purpose, includes return format and usage guidance. Every sentence is necessary without redundancy.

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?

Covers purpose, return format, usage context, and legal disclaimer. The output schema is described inline. It could optionally mention that required fields vary by country, but current content is sufficient for a validation tool with good annotations and schema.

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%, so parameters are well-documented in the schema. The description does not add new semantics beyond mentioning 'mandatory fields', which is implied by the tool's purpose.

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 it validates an invoice JSON for mandatory fields for VAT invoices in European countries, referencing EU Directive. It distinguishes from sibling validation tools (e.g., validate_vat_de, validate_nif) by focusing on invoice schema rather than individual identifiers.

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?

Explicitly recommends use in invoice generation pipelines, pre-submission validation, and compliance checks. While it doesn't list alternatives, the context makes the tool's role clear among siblings.

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