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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds substantive context beyond them: the shape of the returned payload, the fact that totals are in client currency, and the auth requirement (Cotlet API key with access to this app). No contradictory claims.

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?

Content is front-loaded with the return payload described first, then the email-log tip, currency note and auth requirement. It is a bit repetitive, restating 'one invoice' and enumerating the contents twice across the first two sentences, which costs a point.

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?

There is no output schema, so the description must carry the return contract, and it does so in useful detail (line items with fields, contacts, payments, email log with recipient and time). Combined with the auth note, an agent has enough to call and interpret the tool; only the when-to-use routing is thin.

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 both parameters (company, invoice_number) are already fully documented, including the INV-0038 example. The description adds nothing parameter-specific beyond implying a single-invoice lookup. Baseline 3 when the schema does the work.

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 (get) and resource (invoice) and then enumerates exactly what one invoice contains: line items, contacts, linked payments and the email log. An agent can distinguish this from list_invoices or create_invoice without opening any 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?

It gives a real workflow hint ('Use the email log before resending, so a client is not emailed twice in a row'), but that guidance is about a downstream action, not about when to choose this tool over list_invoices or another retrieval tool. No explicit exclusion or alternative is named, so usage is only implied.

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