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

Annotations already establish the safe read-only profile, but the description adds real behavioral detail beyond them: page size bounds and defaults, and the rule that unpaid invoices are those where paid_amount is below total. It omits result ordering and total-count behavior, so not a 5.

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 dense, front-loaded sentences that each carry information, with the auth requirement placed last. Minor redundancy: the status values are enumerated twice, once in the filter sentence and implicitly in the field list.

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 no output schema, the description usefully characterizes the returned items and pagination; there are no required parameters so nothing is left ambiguous for invocation. It could still say how results are ordered or how to detect a final page, which is why it is not a 5.

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 schema already documents page, page_size, status, due_before and customer_id; the description largely restates the status enum and pagination defaults. Its genuine addition (the paid_amount vs total interpretation) concerns returned data rather than input parameters, so baseline 3 is appropriate.

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 ('List invoices of the company') and enumerates the fields each item carries (number, customer, dates, status, amounts). An agent can immediately distinguish it from bokio_get_invoice, which fetches one invoice, without opening the 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?

Gives clear operating context: pagination defaults, the status values that can be filtered, and that customer filtering uses an ID from list_customers. It does not explicitly say when to prefer this over a sibling or when not to use it (e.g. single-invoice lookup), so it falls short of a 5.

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