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

Annotations already declare readOnlyHint=true, so the safety profile is covered; the description goes further by disclosing the auth requirement (Cotlet API key with app access) and the multi-partial-payment behavior ('open shows what is left'), which the annotations do not convey.

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 and reasonably tight, but the first sentence ('One invoice with lines, taxes, total, payments and approval state') largely duplicates the second sentence's enumeration of the same fields, costing a little efficiency.

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 carries the return-shape burden and does so completely: line-level tax/discount, totals, payment history and approval status, plus the auth requirement. An agent has everything needed to call and interpret it.

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% and the single invoice_id parameter is already documented with its source ('from list_invoices'), so the schema does the heavy lifting. The description adds no syntax or format detail beyond it; 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?

Specific verb ('Get') plus resource ('invoice') and an enumeration of exactly what comes back: lines, tax, discount per line, total, payments, approval state. An agent can distinguish it from holded_list_invoices and holded_add_invoice_payment 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?

"Use it before recording a payment or sending a reminder" gives a clear use context that implicitly points at the add-payment and send-invoice siblings. It stops short of naming alternatives or stating exclusions, so it is clear context rather than explicit routing.

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