get_invoice

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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. Beyond that, the description only adds the vague qualifier 'for payment', which is ambiguous rather than informative. It does not disclose what the response contains, whether unpaid invoices differ from paid ones, or any auth/scoping requirements.

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 short sentence with no padding, and the resource ('a specific invoice') appears early. It is well-sized for the tool, though the parenthetical API-method reference is marginally useful 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?

With no output schema and no real behavioral detail, the description leaves the agent guessing what 'data' is returned and how this differs from the large family of related billing/read tools. For a simple one-parameter read this is not catastrophic, but it under-serves a namespace crowded with near-neighbors.

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% for the single required parameter (invoice_id, documented as 'Invoice number'), so the schema fully carries parameter meaning. The description adds nothing about the parameter's format or where the ID comes from, which is the baseline case for high-coverage 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?

It names the resource (a specific invoice) and implies retrieval via 'Data for...', with the underlying API method 'whmcs/get_invoice' as a parenthetical. However, the verb is nominal rather than action-oriented, and with siblings like get_invoices, get_server_invoices, and download_invoice present, it does nothing to distinguish itself from those alternatives.

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 statement of when to use this tool versus get_invoices (list all) or download_invoice (retrieve the document). The phrase 'for payment' hints at a billing context but never says whether this is a pre-payment lookup, a verification step, or what triggers its use. The agent must infer everything from the name.

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