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

Annotations already declare destructiveHint=true, indicating a write operation. The description and entity schema go well beyond this by explaining sparse updates by default, that a Line array replaces all lines, the requirement for a current SyncToken, and prohibited fields (SSN, birth dates, card details). This is rich behavioral disclosure that adds context not present in the annotations, with no contradictions.

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 a single, front-loaded sentence that immediately conveys the verb and resource, and includes the critical requirement (Id and SyncToken). There is no filler or redundancy; it is as concise as possible while still being informative.

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?

The tool is simple with rich schema descriptions covering the entity behavior and the company parameter. The description, while minimal, is sufficient given the schema and annotations. It does not mention response format or side effects, but with no output schema and a clear update action, this is acceptable. The entity schema provides the needed operational details.

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?

The input schema provides 100% coverage with detailed descriptions for both parameters, especially the entity object, which explains required fields, sparse behavior, and prohibited data. The tool description only restates 'requires Id and SyncToken', which is already in the schema, so it adds minimal value beyond the structured definition. The baseline of 3 applies given high schema coverage.

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 clearly states the action (update) and the resource (invoice) with a specific context (QuickBooks Online). It also adds a critical requirement (Id and SyncToken) that differentiates this from create, delete, or void operations. This is a precise, unambiguous purpose statement.

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 for existing invoices by requiring Id and SyncToken, and the entity schema instructs to fetch the invoice first, which gives clear contextual guidance. It also explains sparse vs. full update behavior in the schema, aiding selection of appropriate update semantics. However, it does not explicitly contrast with sibling create/delete/void tools, though the verb 'update' and the existing-entity requirement make the intended use clear.

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