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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds that it accepts an invoice id or number and 'renders an invoice preview', which is useful context, but it does not disclose return format, error behavior, or what happens with invalid identifiers. This is adequate but not rich.

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 sentences, front-loaded with the usage trigger, followed by the accepted input format and the output behavior. Every sentence earns its place; there is no fluff or repetition of the schema or annotations.

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 single-parameter read-only tool with strong annotations, the description covers the main invocation path and expected output. It is complete enough for an agent to call it correctly, though it does not specify failure modes or explicitly route between draft and finalized invoice siblings.

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 schema already labels invoice_id as 'Invoice id or number'. The description adds a concrete example ('INV-0007') and clarifies that either an id or a human-readable number is acceptable, giving the agent more practical guidance than the raw schema alone.

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 uses a specific verb ('get') and resource ('specific invoice'), and lists the exact scope: lines, total, due date, payment link, or payment status. This clearly differentiates it from sibling tools like invoice.list or invoice.preview_draft, which serve different purposes.

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?

The description explicitly opens with 'Use this when the user asks about a specific invoice's...', giving a clear triggering condition. It does not mention when not to use it or name alternatives, such as invoice.preview_draft for drafts or invoice.list for browsing, so it falls just short of a 5.

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