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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds that this is a thin proxy over the Fortnox REST endpoint (with a docs link), which helps an agent anticipate Fortnox-style error semantics, but it says nothing about not-found behavior or what happens with a nonexistent GivenNumber.

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, front-loaded with the verb and resource, then the exact upstream endpoint. No filler and nothing buried.

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?

An output schema exists, annotations are rich, and there is only one parameter, so the description is nearly complete. The remaining gap is that it does not state how this differs from the sibling invoice-lookup tools or what a missing invoice returns.

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% for the single parameter, so the schema already documents GivenNumber. The URL template hints that GivenNumber is a path segment (number or string), which is marginal added value beyond the schema; 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 gives a specific verb + resource ("Retrieve a single supplier invoice") and the word "single" implies contrast with list_supplier_invoices / find_supplier_invoices. It never names those siblings explicitly, so the differentiation 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?

Usage is only implied: the URL template GET /3/supplierinvoices/{GivenNumber} signals an identifier-based lookup rather than a search, but there is no explicit when-to-use/when-not and no pointer to find_supplier_invoices or list_supplier_invoices as alternatives.

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