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

Opens with 'MUTATES Quaderno data', consistent with the destructiveHint=true annotation, and adds genuinely new context beyond it: the POST endpoint and the fact that the created invoice (with permalink and pdf) is returned. No contradiction with 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-loads the mutation warning and the required inputs, then endpoint and return value. Slightly redundant on the item shape, which the schema already documents, but overall dense and well-ordered.

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, and the description compensates by saying what is returned (created invoice incl. permalink, pdf). For a nested-object mutation tool with zero required params, it covers inputs, escape hatch, and response adequately.

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 already 100%, so baseline is 3, but the description adds value by enumerating the concrete attributes usable in `fields` (currency, issue_date, due_date, po_number, notes, tag_list, custom_metadata, payment_details) and sketching item keys with optional markers.

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 ('create an invoice for a contact') and gives the underlying endpoint POST /invoices, so the agent knows exactly what is produced. It never names a sibling to contrast with (e.g. create_transaction vs create_invoice), so it stops short of full sibling differentiation.

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?

Clear invocation context: supply contact_id (or a full contact via `fields`) plus items, and use `fields` as the escape hatch for anything else. It doesn't state when to prefer this over alternatives such as create_transaction, but the prerequisites are explicit.

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