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 useful return-content context (type, series, number, PDF link, collections for invoices), which partly compensates for the missing output schema, but says nothing about auth, error behavior, or what a missing document returns.

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, front-loaded with what the tool returns and the keying scheme. The trailing raw endpoint 'GET /api/docs/<type>' is marginally useful but is the only slightly extraneous element.

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 correctly steps in to summarize the returned fields (type, series, number, PDF link, collections). Combined with 100% schema coverage and a readOnly annotation, an agent has enough to invoke it correctly, though usage routing remains thin.

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%, so every parameter is already documented with examples and formats. The description merely echoes type/series/number without adding format, syntax, or edge-case detail beyond the schema, making the baseline 3 correct.

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: retrieves ONE invoice, proforma or notice identified by series and number. The singular framing implicitly contrasts with the list-oriented siblings (oblio_list_invoices), but no sibling is named explicitly, so it stops 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?

The description says how the document is keyed but never states when to use this tool versus oblio_list_invoices or the create/cancel/restore siblings. No prerequisites or exclusions are given; the only routing hints (oblio_list_companies, oblio_list_series) live 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.