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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the write/safety profile is covered. The description adds one genuinely useful behavioral fact beyond the annotations: the call returns the saved record including its SyncToken, which is needed for any follow-up update. It still says nothing about validation failures, PII rejection behavior mentioned in the schema, or whether duplicate submissions create duplicates.

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?

Two short sentences with the verb and result front-loaded; every clause carries information and nothing is padded or repeated from the title.

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 whose annotations carry the safety profile and whose schema fully documents the entity payload, the description covers the essentials and even notes the returned SyncToken. The remaining gap is disambiguation from the other purchase-like create tools, which is the main thing an agent could get wrong here.

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%, so the entity parameter's required PaymentType/AccountRef fields and the PII prohibition are already documented in the schema. The description adds nothing about parameters, so the baseline 3 applies.

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 and resource ('Create a purchase') and scopes it to QuickBooks Online, so the agent knows exactly what entity is being created. However, it does nothing to distinguish a Purchase from the many easily-confused siblings (create_purchase_order, create_bill, create_expense-style tools, create_sales_receipt), which matters in this crowded namespace.

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 offers no when-to-use guidance, no prerequisites, and never names an alternative tool. With siblings like create_purchase_order and create_bill sitting right next to it, the absence of any routing hint leaves the agent to guess which create tool applies.

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