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 the auth requirement ('Needs the user's Cotlet API key with access to this app') plus the shape of the returned data. With no output schema, that return-value context is valuable, though it omits pagination or line-count behavior.

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?

Three tight sentences, front-loaded with what it returns and following with usage and auth, with no filler. Slightly more compact phrasing could merge the return-contents detail, but every sentence earns its place.

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?

For a read-only 2-param tool with no output schema, the description adequately covers the return payload, the auth prerequisite, and the intended workflow with send_sales_invoice. Only minor gaps remain (no mention of draft vs sent status semantics in the response or error cases).

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 (division, invoice_id) are already documented with their sources (list_divisions, list_sales_invoices/create_sales_invoice). The description only restates 'by invoice ID' and adds no format or default details beyond the schema, so 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 verb ('Returns') and resource ('one sales invoice'), and enumerates the returned contents (header, every line: description, quantity, unit price, VAT code). It implicitly contrasts with list_sales_invoices (one by ID, not a list) and names a sibling (send_sales_invoice), so an agent can distinguish it without opening the 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?

Gives explicit usage context ('Use it to check a draft before send_sales_invoice'), naming the downstream alternative and the condition that motivates the call. It lacks an explicit when-not-to-use statement or a pointer to list_sales_invoices for retrieval by other criteria.

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