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

Annotations declare destructiveHint=true, readOnlyHint=false, and openWorldHint=false, so the mutation and safety profile are already covered. The description adds useful behavioral context: it requires the current SyncToken for optimistic concurrency and returns the saved record with a new SyncToken. It does not describe sparse-update semantics, which are left to the schema.

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 sentences with no wasted words. The action is front-loaded, prerequisites are parenthetically placed, and the return behavior is stated briefly and usefully.

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 description covers the essential points: it updates an existing bill, requires an Id and current SyncToken, and returns the saved record with a new SyncToken. Given the rich 100%-covered input schema for the nested entity object and annotations that already flag destructiveness, no critical information is missing, though it could mention sparse-update implications at a high level.

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 100%, so the input schema already fully documents both parameters, including the nested entity fields, required Id, SyncToken, sparse update behavior, and VendorRef requirement. The description only restates the Id and SyncToken requirement, adding no semantics beyond the schema, 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 (update) and resource (existing bill) in a named system (QuickBooks Online). Clearly distinguishes from create_bill, get_bill, delete_bill, and update_bill_payment by resource and action.

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 the tool is used to modify an already-existing bill and notes the required Id and current SyncToken, which implies you must fetch the bill first. It does not explicitly name alternatives or when not to use it, but the prerequisite gives clear context.

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