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

Annotations declare destructiveHint=true and readOnlyHint=false, so the safety profile is already structured; the description adds genuinely new behavior — this is an optimistic-concurrency write keyed on SyncToken — and discloses the return value including the new SyncToken for chaining. It doesn't cover the sparse-vs-full update semantics, but those live in 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?

A single sentence, no filler, front-loaded with the action, scope, and the blocking precondition, then the return. Nothing to trim.

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?

Even without an output schema the description states the return shape (saved record plus new SyncToken), which is what an agent needs for follow-up calls. The only gap is that it does not restate the destructive/sparse-write implications, which annotations and the rich schema already carry.

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 schema already explains Id/SyncToken, sparse semantics, VendorRef repetition and forbidden government identifiers. The description repeats the Id+SyncToken requirement without adding format or syntactic detail, 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 (vendor credit) plus the product scope (QuickBooks Online), which cleanly separates it from create_vendor_credit, delete_vendor_credit, get_vendor_credit and the many other *vendor_credit siblings. The concurrency precondition (Id + current SyncToken) is named up front, so an agent knows what state it must already hold.

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?

It gives a prerequisite (fetch the record first to get the current SyncToken) which implies the workflow, but never says when to choose update over create/delete or what to do if the SyncToken is stale. That is implied guidance rather than explicit when/when-not routing.

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