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

The input schema adds substantial behavioral detail beyond the destructiveHint annotation: sparse updates are the default, a Line array replaces all lines, and sparse:false clears every writable field left out. It also warns against sending government IDs, birth dates, or card-processing details, which is valuable operational context for an agent.

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 top-level description is a single front-loaded sentence with no wasted words. The longer entity description is dense but each sentence earns its place by explaining update semantics, destructive behavior, or sensitive-field restrictions.

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 destructive mutation tool with nested parameters, the definition covers prerequisites, sparse vs. full update behavior, line replacement, and sensitive-field handling. It does not describe the return value, but with no output schema specified for this update operation, that is a minor gap.

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 the entity parameter description thoroughly documents requirements, sparse semantics, and sensitive-field restrictions. The tool-level description adds no additional parameter meaning, so the baseline of 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?

The description names a specific verb ('Update'), a resource ('purchase order'), and a scope ('existing ... in QuickBooks Online'), which clearly distinguishes it from create or send operations. It does not explicitly contrast sibling tools, so it falls just short of a 5.

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 states the core precondition ('requires Id and SyncToken'), and the entity schema reinforces it with 'fetch the PurchaseOrder first.' This gives clear context for when the tool is appropriate, though it does not explicitly name alternatives like create_purchase_order or get_purchase_order.

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