download_invoice

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

Annotations already mark the tool as read-only, so the bar for additional disclosure is lower. The description adds a concrete behavioral detail beyond the schema: the response typically contains a PDF in Base64 and should be saved/decoded. The 'usually' caveat also warns about possible format variability.

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?

A single sentence that front-loads the action, states the endpoint, and then gives the essential post-processing instruction. Every part earns its place with 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 one-parameter, read-only download tool with no output schema, the description is complete: it states what will be returned (Base64 PDF) and what to do with it. Parameter requirements are fully covered by the schema, and no extra operational context is needed.

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% and the single invoice_id parameter is already described as the invoice number. The description adds no parameter-specific meaning, so it matches the baseline for fully documented schemas.

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 opens with a concrete action and resource: 'Download invoice to PDF' and gives the exact endpoint whmcs/download_invoice. It also names the output format (PDF), which distinguishes it from sibling invoice lookups such as get_invoice/get_invoices.

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?

Usage is implied by the purpose: use this when you need the invoice as a downloadable PDF. There is no explicit 'when not to use' or comparison with get_invoice/get_invoices, so routing to alternatives is left to inference.

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