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

Goes well beyond the readOnly/idempotent/closed-world annotations by disclosing two operationally critical facts: it consumes one metered call (quota cost) and requires an InvoiceVerify account with OAuth sign-in (auth prerequisite). It also describes the response shape (pass/fail, rule IDs, line numbers, fixes), which matters since there is no output schema.

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 front-loads the supported formats and rule sets, then the return value, then the cost and auth constraints. Every clause carries information an agent needs; nothing is redundant with the title or schema.

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?

For a two-parameter, non-destructive validation tool, the description covers the gaps that structured data leaves: quota cost, authentication requirement, and return contents. With 100% schema coverage and annotations carrying the safety profile, no material question is left open before invocation.

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%, so both xml and profile are already fully documented, including the 'auto' detection behavior via CustomizationID. The description names the supported formats, which loosely relates to the profile enum, but adds no syntax or size guidance beyond the schema. Baseline 3 applies.

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?

Specific verb (validate) plus the exact resource and supported syntaxes (UBL 2.1, Peppol BIS Billing 3.0, XRechnung, CII/Factur-X) and the rule sets checked (EN 16931, Peppol). This clearly separates it from siblings like convert_invoice and parse_invoice, which transform or extract rather than check compliance.

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 clear context for invocation: you have an invoice XML and want a pass/fail compliance verdict with rule IDs. It stops short of explicitly routing the agent away from parse_invoice or convert_invoice when those are the better first step, and states no exclusions.

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