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

readOnlyHint=true already tells the agent this is a safe read. The description adds that the response is complete ('all fields', enumerating blocks), which is useful, but it says nothing about auth requirements, not-found/error behavior, or id provenance beyond the endpoint path. Adequate but not rich against the annotation baseline.

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?

Front-loaded with the key fact ('One document with all fields') followed by a compact field enumeration and endpoint. Dense but every clause carries information, especially since no output schema exists to carry the field list.

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 field enumeration (supplier/customer blocks, items, totals, flags, URLs) does the heavy lifting of describing the return value, which is genuinely valuable. For a low-complexity single-id read tool this is nearly complete, though it omits error/not-found context.

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 coverage is 100% and the single id parameter is already fully documented in the schema (including its origin from list_invoices). The 'GET /invoice/{id}/' fragment only re-confirms that id is a path parameter, adding little beyond 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?

The description conveys that the tool returns a single full invoice document ('One document with all fields'), which implicitly distinguishes it from the list siblings. However, it never states the action explicitly (e.g. 'retrieve a single invoice by id') and instead reads as a field inventory, so the purpose is inferred rather than stated.

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 when-to-use guidance and no mention of alternatives, even though vyfakturuj_list_invoices exists as the obvious alternative for multiple invoices. The agent must infer that this is for fetching one invoice by id.

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