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

Annotations declare destructiveHint=true, and the description reinforces this by saying values are 'overwritten' rather than merged, plus discloses the customerId side effect that auto-populates recipient data. It does not cover auth/permission requirements, but the destructive semantics and the 'does not submit' boundary add real context beyond the 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?

Three tight sentences, front-loaded with the core action; the 'Does not submit' line at the end is a useful disambiguator rather than filler. Minor redundancy with the schema on the customerId behavior keeps it from a 5.

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 mutation tool with no output schema, the description covers the essentials: overwrite behavior, draft-only scope, and the key side effect. It stops short of stating whether unmentioned fields are preserved and what permissions are needed, which would round it out.

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 67% and the schema already documents the customerId auto-population ('Recipient data is auto-populated from the customer'), so that note is largely redundant. The description gestures at 'dates, currency, and notes' but adds no syntax or format detail, and several fields (invoiceNumber, paymentMethods, includeTaxIntoPrice, supply dates) are unmentioned. Baseline 3 is appropriate.

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 ('Update existing fields on a draft invoice') and a scope boundary ('Does not submit the invoice') that cleanly separates it from submit-invoice. The overwrite semantics and draft-only scope let an agent distinguish it from create-invoice-draft and duplicate-invoice without opening schemas.

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 positions the tool in the workflow: 'Set lineItems, dates, currency, and notes here before submitting,' which tells the agent this is the pre-submission editing step. It rules out submission but does not explicitly name submit-invoice as the alternative or state prerequisites (e.g., that the invoice must already be a draft).

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