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

With no annotations, the description carries the full burden. It does disclose the return encoding (base64 PDF) and included content, which is valuable, but says nothing about read-only nature, permissions, error behavior for missing/draft invoices, or size constraints.

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 efficient sentences, front-loaded with the return format and contents, followed by a practical usage hint. No 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 simple single-parameter read/render tool with no output schema and no annotations, the description covers what is returned but omits safety profile, error semantics, and any notes about invoice state or authentication.

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 0%, so the description should compensate, yet it says nothing about invoice_id. The parameter is fairly self-evident from the tool name, but the description adds no meaning such as UUID source or lookup behavior.

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/resource: renders the invoice as a PDF (base64) and enumerates its contents (shop, customer, lines, paid, balance). This clearly differentiates it from invoices_get, which returns invoice data rather than a rendered document, though it doesn't name that sibling explicitly.

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?

"Attach it to email or save it" implies the intended use for downstream delivery, but it gives no explicit when-to-use vs invoices_get/invoices_send guidance and no exclusions or prerequisites.

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