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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description contributes the required scope, which is genuine added context, but says nothing about behavior on a missing/invalid id or about partial results when embed scopes are absent.

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 sentences with zero filler: the operation and return shape come first, then the required scope. 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 single-record read with full annotation coverage and a fully documented schema, this is close to sufficient; it even summarizes the return payload despite there being no output schema. The remaining gap is that it does not help the agent find an id when one is unknown.

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 the parameter semantics baseline is 3. The only parameter mentioned in the description is id ('by id'); embed and field, including the caveat that embed targets are null without extra scope, are handled entirely by the schema.

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 and resource ('Get one invoice by id') and enumerates the payload it returns ('its rows, amounts and status'). The 'by id' / 'one' framing implicitly distinguishes it from sellsy_list_invoices and sellsy_search_invoices, though it never names them explicitly.

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?

Adds a real prerequisite ('Needs invoices.read') that tells the agent an auth scope is required before calling. However, it gives no guidance on when to prefer this over the sibling lookup tools (search_invoices, list_invoices) when the id is unknown.

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