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

Annotations already declare readOnlyHint, idempotentHint and non-destructive, so safety is covered. The description adds value beyond that by disclosing the required billing:read permission and the account/MCP-key requirement, and notes the response includes invoice lines.

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 tight fragments with the resource and identifier options front-loaded; no filler. Slightly telegraphic, but every clause earns its place.

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 read-only getter with annotations covering safety and no output schema, the definition supplies the key facts: single-invoice scope, accepted identifier forms, required scope, and account prerequisite. Return-shape detail is minimal but the description notes 'its lines'.

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 coverage is 0% and the lone invoiceId parameter has no schema description. The description compensates by explaining it accepts either an internal id or an invoice number, which is meaningful format guidance the schema omits.

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 (get) and resource (invoice) and narrows scope to a single invoice 'with its lines', implicitly distinguishing it from the sibling gpucloud_list_invoices. It never names the sibling explicitly, so it is clear but not fully differentiated.

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: fetch one invoice when you already have its id or number. There is no explicit when-to-use vs when-to-prefer-list_invoices guidance or stated prerequisites beyond the account requirement.

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