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

Annotations already confirm readOnly, openWorld, and non-destructive behavior, and the description adds substantial operational context: exact XML parsing versus Claude Haiku for PDF/photo, VIES VAT ID and IBAN/BIC validation, EN 16931 detection, 15 MB size limit, and the $0.02 USDC per-call x402 payment mechanism.

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 front-loaded with purpose and then adds operational details in a dense but mostly useful single paragraph. Every sentence is relevant, though the payment and sample details could be slightly more structured.

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 no output schema, the description compensates by listing the extracted JSON fields, validation checks, and e-invoice authenticity signal. It also covers input limits, pricing, and a free sample, leaving no major gap for correct 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 the baseline is 3. The description adds a meaningful input constraint (up to 15 MB), identifies supported input formats, and provides a concrete example invocation using pdf_url, which helps an agent understand parameter usage beyond the schema text.

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 states a specific verb and resource: invoice data extraction from PDFs, photos, and EU e-invoice XML into structured JSON. It identifies the exact document domain (accounting invoices) and distinguishes its behavior from generic OCR or PDF extraction by explaining that e-invoices are read from embedded XML without AI.

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 when to use it: accounting agents processing PDF, photo, XRechnung, ZUGFeRD, or Factur-X invoice inputs. It does not explicitly name sibling alternatives such as pdf_extract or ocr, but its format-specific processing notes provide practical routing guidance.

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