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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds non-obvious behavior: newest-first ordering, the default status filter, that amount due is total minus recorded payments, and that a Cotlet API key with app access is required.

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 core action and the returned fields, then the defaults and the overdue trick. Dense and mostly waste-free, though the opening field list reads as a slightly run-on enumeration.

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 documents the returned fields, sort order, default behavior, and auth requirement. Nothing an agent needs to select or invoke this filtered-list tool 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 coverage is 100%, so the baseline is 3. The description still adds interpretation beyond the schema text: it explains the overdue use case for older_than_days and the derivation of the amount-due field, which the schema does not.

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 ('Lists invoices') and resource, and enumerates the fields each record carries (customer, total, amount due, due date, status) plus sort order. Clear what it does, though it does not name or distinguish itself from siblings like yardbook_get_invoice.

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 real actionable context: status defaults to unpaid, and older_than_days is explicitly framed as 'how you find overdue ones.' It stops short of naming alternatives or stating when not to use it, so it is clear context without explicit exclusion routing.

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