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

Annotations already cover the safety profile (readOnly, non-destructive, openWorld), and the description adds real value on top: what is returned (every line with description/amount/account, total, status), that total equals the sum of lines, and that a Cotlet API key with app access is required. Auth requirement disclosure is meaningful beyond the annotations.

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?

Short and front-loaded, leading with the resource and return shape before the usage hint. The first two sentences overlap ('One AP bill with its lines...' / 'Returns one AP bill with every line...'), a minor redundancy, but overall there is little waste.

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 correctly carries the burden of describing the return structure (lines, total, status), plus auth and usage context. For a single-param read tool this is largely complete; only a link to the list tools for obtaining the reference is left implicit.

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%; the schema already documents reference_nbr and even its source (list_invoices or list_bills). The description adds no parameter-level meaning, so the baseline 3 applies.

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 clear verb+resource ('One AP bill with its lines, total and status') and uses 'AP bill' to distinguish it from the AR sibling get_invoice and the plural list_bills. It does not explicitly name those alternatives, but the resource is specific enough that an agent can tell what it retrieves.

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 a concrete usage condition: 'Use it before approving or releasing a bill,' which ties directly to the approve_bill_for_payment and release_ap_bill siblings. No explicit when-not-to-use or named-alternative guidance, so it stops 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.