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

With no annotations, the description carries the full transparency burden and does well: it discloses partial-update behavior, the forward-only constraint on nextNumber, and the practical consequence of omitting paymentInstructions. It stops short of covering permissions, validation errors, or return values, but the most operationally critical behaviors are surfaced.

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?

The description is three sentences and front-loaded with purpose and core behavior. Each sentence earns its place: the partial-update rule, the paymentInstructions warning, and the nextNumber forward-only constraint. There is no filler or repetition of schema content.

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 13-parameter settings update with no required fields, no output schema, and no annotations, the description handles the main invocation hazards: optionality, the payment-instructions consequence, and the nextNumber monotonic constraint. It is not exhaustive about every field or failure mode, but the essential correctness rules are covered.

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?

Input schema coverage is only 38%, so the description must compensate. It adds meaningful semantics for paymentInstructions and nextNumber, explaining consequences not present in the schema. The other 11 parameters are left to their self-explanatory names, with no added format, default, or boundary guidance beyond what the schema already gives.

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?

The description opens with a specific verb and resource: 'Change what appears on invoices.' It clearly communicates this is a settings-update operation distinct from invoice_settings_get and from draft-invoice mutations. It doesn't explicitly name a sibling, but the scope is unambiguous.

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 implies usage by stating 'Only the fields you pass are touched,' which is an important update pattern. However, it never explicitly compares against alternatives like invoice_settings_get, invoices_create_draft, or invoices_update_draft, or says when not to use this tool. Guidance is present but implied rather than explicit.

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