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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered; the description adds real value by disclosing the response contents (totals, balance, line items, PDF links) since no output schema exists. It does not mention auth requirements or pagination, but for a single-resource GET that gap is minor.

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 compact sentences: the return surface is front-loaded and the expand behavior plus endpoint follow. No filler, no repetition of the title.

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, the enumerated field list is what makes this definition usable, and it is present. The endpoint path and expand semantics round it out; only edge concerns like permissions or error behavior are absent.

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%, so both parameters are already documented, making 3 the baseline. The description adds only a light gloss on expand ('replaces ids with full objects') that largely restates the schema's 'expand into full objects' and the enum example already present.

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) with scope ('One invoice by id'), which implicitly and effectively separates it from invoiced_list_invoices. It also enumerates the returned data surface, so an agent knows exactly what this call yields.

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 'by id' and the sibling list makes the list-vs-get split inferable, but the description never states when to prefer this tool over invoiced_list_invoices or invoiced_get_credit_note. The only routing hint (find the id with invoiced_list_invoices) lives in the schema, not the description.

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