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 beyond that by disclosing the shape of the returned data (ditto the payments list with due dates and paid status) and the auth prerequisite ('Cotlet API key with access to this app'), which an agent needs for planning. It omits any note on errors/not-found behavior, keeping it at 4.

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?

Four short sentences, front-loaded with the core action, then return contents, then usage, then prerequisites. The enumerated return fields are slightly list-like but still earn their place since no output schema exists.

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 carries the burden of describing return values, which it does in detail, and it adds usage and auth context. It is essentially complete for a read tool; only a note on failure modes (e.g. unknown invoice_id) 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 description coverage is 100% and both parameters (company_id, invoice_id) are documented in the schema, including where invoice_id comes from. The description adds no parameter-level meaning, 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 verb+resource ('Get one invoice') and enumerates what the resource contains (lines, totals, payments, client, VAT). This clearly separates it from siblings like fatture-in-cloud_list_invoices and create_invoice without needing to open 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?

Explicitly tells the agent when to reach for this tool: 'before recording a payment or building a reminder,' which maps to the record_invoice_payment sibling. It stops short of naming the alternative (list_invoices) or stating when NOT to use it, so it is clear context rather than full routing guidance.

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