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

readOnlyHint=true already establishes the safe-read profile, so the bar is lower, yet the description still adds genuinely useful negative disclosure: the public access token and payment links are NOT returned. It also names the underlying endpoint GET /invoices/view/{id}.json. It does not disclose auth requirements or error behavior for missing/unauthorized ids.

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 short sentences plus a bare endpoint reference carry a lot of information with no padding. The returned-content enumeration is front-loaded, and the exclusion note is placed where it is most useful.

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 description carries the return-value burden and does so well by listing the component sections of the returned document. It stops short of covering error cases (invalid id, permissions) or whether embedded items/payments can be large, but it is otherwise sufficient for a one-parameter read tool.

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% with a single required invoice_id, so the schema already carries the parameter burden. The description adds no format, range, or provenance detail for invoice_id beyond what the schema states, so the baseline 3 applies.

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 clearly indicates retrieval of a single document and enumerates what it contains (header, client, items, VAT summary, payments, related documents), which distinguishes it from the sibling superfaktura_list_invoices. The verb 'get' is only implicit in the name rather than stated in the description text, so it falls just short of a 5.

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?

There is no guidance on when to use this versus superfaktura_list_invoices or the other get_* siblings, and no mention of prerequisites such as needing an id obtained from the list endpoint. The only such hint ('the id of a superfaktura_list_invoices row') 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.