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

Annotations already cover the safety profile (readOnly, non-destructive), but the description adds real behavioral substance: it defines what a 'payment' versus a 'matched transaction' means, notes e-invoicing status is included conditionally, and states the auth requirement (Cotlet API key with app access). That is meaningful context 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?

Front-loaded with the return content, which is good, but the first two sentences are largely redundant ('One customer invoice with its lines, payments and matched bank transactions' then 'Returns one invoice with every line, the payments...'). The scaffolding sentence wastes space.

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 burden of explaining return values and does so well by enumerating lines, payments, matched transactions and conditional e-invoicing status, plus auth requirements. Only missing usage routing, which is a separate dimension.

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 invoice_id is fully documented in the schema (sourced from list_customer_invoices or create_customer_invoice). The description adds no parameter semantics beyond that, 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 specific resource (one customer invoice) and enumerates the returned content (lines, payments, matched transactions, e-invoicing status). The singular framing implicitly differentiates it from the sibling list_customer_invoices, though it never names the alternative explicitly.

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?

The description gives no when-to-use guidance or routing cues. It never says to use this to fetch a single invoice by ID versus list_customer_invoices, nor when this retrieval is warranted. A capable agent can infer it, but the definition supplies nothing.

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