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

Annotations already establish readOnly, idempotent, non-destructive, and closed-world behavior. The description's added value is the 'attached file' return modality, which is genuinely beyond the annotations, but it says nothing about permissions, error behavior for a missing invoice, or file size/type 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?

One short sentence, front-loaded with the verb and resource, with the useful 'attached file' detail last. No filler or 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?

For a one-parameter read tool with no output schema this is nearly adequate, but the complete silence on the required identifier's origin and on failure modes leaves a real gap. A single clause about where invoiceId comes from would make it whole.

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% for the single required parameter, so the description carries the burden and does not meet it. 'Of an invoice' loosely implies invoiceId identifies the invoice, but no format, source, or retrieval hint (e.g., where to obtain a valid id) is provided.

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?

Names a specific verb ('Get'), resource ('the PDF of an invoice'), and delivery form ('as an attached file'), which separates it from the metadata-oriented get_invoice. It stops short of naming the sibling it complements, so an agent must infer the get_invoice vs get_quote_pdf vs get_invoice_pdf split.

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?

There is no explicit when-to-use or when-not-to-use guidance and no named alternative. The agent is left to infer that this is the binary-download counterpart to get_invoice rather than the record fetch.

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