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

Annotations already declare readOnly, idempotent, non-destructive, so safety is covered. The description adds one real behavioral fact beyond them – result pagination ('one page per call') – and points to the upstream API docs, but says nothing about default page size, ordering, or what the summarize block returns in aggregate.

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?

Three short sentences, front-loaded with the purpose and immediately followed by the pagination caveat. The bare API URL is mild filler, but nothing else is wasted.

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?

For a 35-parameter list tool with low schema coverage, the description is far too thin – an agent gets no sense of the available filters or how they combine. The output schema being present relieves it of return-value explanation, but the parameter gap is the dominant incompleteness.

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?

35 parameters with only ~17% schema description coverage, yet the description explains just one nested field (summarize.all_pages). The 30+ filter params (ocr, sent, credit, fromdate/todate, invoicetype, etc.) and pagination params (limit, offset, page) are left entirely undocumented in both schema and description.

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 list of invoices') and anchors it to the Fortnox endpoint GET /3/invoices. It does not distinguish itself from close siblings like find_customer_invoices or get_invoice, so an agent cannot tell from the description alone which invoice-retrieval tool to pick.

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 'one page per call' note plus 'use summarize.all_pages for totals over every page' implies when server-side aggregation is preferable, which is genuine guidance. However, there is no explicit when-to-use/when-not guidance versus siblings such as list_invoices vs find_customer_invoices vs find_supplier_invoices.

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