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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered. The description adds genuinely non-structured context: a metered-call cost implication and a required InvoiceVerify account with OAuth sign-in, which an agent needs before invoking. It stops short of describing error behavior or input validation failures, keeping it below a 5.

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 tightly packed sentences, front-loaded with the core action and formats before cost and auth requirements. Zero filler.

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 read-only, single-parameter tool with no output schema, the description covers input formats, the output structure (parties, lines, VAT, totals, payment), cost model, and auth prerequisite. An agent has everything needed to call it correctly.

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?

With a single parameter at 100% schema coverage, the baseline is 3, but the description adds real meaning beyond the schema's 'The invoice XML.' by specifying which XML syntaxes are accepted (UBL, CII, Factur-X). It doesn't cover the 5MB size limit or encoding expectations, which the schema only partially implies.

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 (Read) and resource (UBL/CII/Factur-X invoice XML) plus the conversion target (structured JSON with named sections). The naming of supported formats and output shape clearly distinguishes it from siblings like convert_invoice and validate_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?

Gives clear usage context ('for booking or reconciliation') and a cost signal ('Uses one metered call'), which helps an agent weigh it against alternatives. However, it never explicitly names when to prefer validate_invoice or convert_invoice instead, so the routing guidance is implicit rather than explicit.

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