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

No annotations are provided, so the description carries the burden of behavioral disclosure. 'Fetch' implies read-only and the description names the returned data, but it says nothing about error behavior, authorization, or side effects. This is minimal but not misleading.

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?

The description is a single efficient sentence with no filler, repetition of schema fields, or unnecessary clauses. It is front-loaded with the verb and object, and every word adds meaning.

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 single-parameter retrieval with no output schema or annotations, the description covers the object and its return content. It lacks details like not-found behavior or authentication requirements, but these are minor for a fetch operation and largely inferable from the domain.

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?

The schema has one `id` string parameter with 0% description coverage, and the description does not explicitly state that `id` is the invoice identifier. The tool name and 'one invoice' make this inferable, but the description does not fully compensate for the missing schema documentation. The single obvious parameter mitigates the gap.

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 ('Fetch'), names the resource ('one invoice'), and enumerates the included content ('line items, charges, totals and amount paid'). This clearly distinguishes the tool from sibling invoice tools such as invoices_list, invoices_send, and invoices_void without needing to inspect their schemas.

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 intent is clear: retrieve a single invoice by its id. However, the description does not explicitly compare with invoices_list or state when not to use this tool. It provides adequate context but no exclusions or explicit alternatives, so it misses the top mark.

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