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

Annotations already declare readOnly, idempotent, non-destructive and non-openWorld, so the safety profile is covered. The description adds only the upstream endpoint and a docs link — useful provenance, but it says nothing about not-found behavior, error shapes, or whether financial-year scoping changes the lookup.

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 with the purpose front-loaded; the API endpoint and docs link earn their place as provenance for a thin Fortnox wrapper. Slightly redundant given the title repeats the same sentence.

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 an output schema present and complete param descriptions, an agent has everything needed to invoke it correctly. The only gap is behavioral context around missing vouchers and the financialyear filter, which is minor for a simple GET-by-id 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 coverage is 100%, so the baseline is 3. The URL template does clarify that VoucherSeries and VoucherNumber are the identifying path segments (a small real addition), but the optional financialyear filter is never mentioned in the description, and no format or type guidance is added.

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 ('Retrieve a specific voucher'), and the singular 'specific' plus the URL template with both key segments makes it distinguishable from list_vouchers. It stops short of naming the list sibling explicitly, but the read-one semantics are unambiguous.

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 REST path implies lookup-by-key semantics (you must already know series and number), which is useful implied guidance, but the description never states when to use this versus list_vouchers or find_vouchers_without_attachments, nor what to do if the voucher is missing.

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