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

Annotations already establish a safe read-only, non-destructive operation. The description adds real behavioral context beyond them: page size ceiling (100), ordering that mirrors the Fortnox UI list, totals-only payloads, and the auth requirement (Cotlet API key with app access). A minor gap is no explicit mention of pagination via cursor beyond the schema's own cursor field.

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 its fields, then filtering guidance, then the get_invoice hand-off and operational constraints. Dense but nearly every sentence carries information; the opening fragment is slightly clipped but not wasteful.

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 read-only list tool with no output schema, the description covers what each item contains, ordering, page size, auth needs, and the alternative tool for detail. Nothing essential to calling it correctly is missing.

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 description coverage is 100%, so the baseline is 3. The description earns a bump by defining the 'overdue' status semantics (unpaid plus past due date), which the enum alone does not convey, and by tying status/customer filtering to a goal. Remaining params (limit, cursor, due_before) are left entirely to the schema.

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+resource (lists customer invoices) and enumerates the fields each item holds (number, customer, dates, total, remaining balance). It also clearly distinguishes itself from get_invoice, which returns the rows, so an agent can tell the two apart without opening a schema.

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 tells the agent to filter by customer or status to find unpaid/overdue invoices, defines 'overdue' (unpaid and past due date), and routes to get_invoice when line-level rows are needed. This is strong when-to-use and alternative routing.

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