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

Annotations already declare the read-only safety profile, but the description adds substantial context beyond them: sort order (oldest due date first), page capacity (up to 100), the totals-only granularity of each item, and the Cotlet API key/app-access requirement. These are exactly the traits an agent needs before calling.

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 resource and returned fields, then filters, then alternatives, then pagination and auth. Dense but every sentence carries information; only slight redundancy between the status explanation and the schema enum keeps it from a 5.

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?

There is no output schema, so the description carries the return-shape burden and does so (per-invoice fields and totals-only scope). Combined with pagination size, ordering, filter semantics, and the auth prerequisite, an agent has everything needed to call this correctly.

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, but the description adds real meaning beyond the enum: 'overdue means unpaid and past the due date' and 'draft returns the drafts shown under Utkast in Fiken'. The limit's 1–100 range is echoed as 'pages hold up to 100' but cursor/due_before/customer_id get no extra explanation.

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 ('Lists the invoices of the company') plus the exact fields returned (number, customer, dates, gross amount, remaining balance) and the sort order. It is clearly distinguishable from fiken_get_invoice, which it names as the detail counterpart.

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?

Explicitly routes the agent: use status filters to find unpaid/overdue invoices, and use get_invoice when lines and payments are needed rather than list items. The condition that selects the alternative is stated, not left to inference.

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