get_invoice_pdf

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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so the bar is lower. The description still adds real value beyond them: it discloses that the PDF is returned as an attachment on the answer and that nothing is written to disk, which is exactly the delivery detail an agent needs and no annotation conveys.

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 short sentences, zero filler, and the identification of the resource and its key comes first, followed by the delivery mechanic. Nothing could be removed without losing information.

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 read tool with full schema coverage, the definition covers the essentials, and since there is no output schema, the note that the PDF arrives attached to the answer usefully fills the return-value gap. Only the routing versus get_invoice_data/list_invoices is left unstated.

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 parameters are already documented in the schema, including the company default and the list_companies pointer. The description only echoes that lookup is by invoice number, adding no syntax or format detail beyond the schema example. 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?

States a specific resource and lookup key: 'PDF of an existing outgoing invoice by invoice number.' An agent can distinguish it from get_invoice_data (structured data) and list_invoices (enumeration) by the 'PDF' output, though the description never explicitly contrasts them.

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?

'existing outgoing invoice' implies scope (not drafts or proforma) and the required invoice number implies lookup-by-identifier, but the description never states when to prefer this over get_invoice_data or how to obtain a valid invoice number via list_invoices. Usage is inferable rather than explicit.

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