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

Annotations already declare readOnlyHint=false and destructiveHint=true. The description adds beyond that by disclosing SyncToken rotation (the transaction returns a new SyncToken), which tells the agent the token is invalidated after the call and concurrency matters. Richer detail (sparse vs. full update, field clearing) lives only 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?

Two sentences, front-loaded with the action, then the prerequisite, then the return value. No filler; the parenthetical is slightly dense but earns its place by explaining SyncToken currency.

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?

With no output schema, stating that the saved record and its new SyncToken are returned is necessary and present. Combined with the schema's coverage of sparse/full update semantics and the cannot-delete/Active:false constraint, an agent has enough to call this tool correctly.

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 carries the heavy lifting on both 'entity' and 'company'. The description only restates the Id/SyncToken requirement and adds the provenance of the SyncToken, which is marginal added meaning.

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 ('Update an existing vendor in QuickBooks Online'), and the word 'existing' implicitly separates it from create_vendor. It does not name any sibling explicitly, so an agent must infer the boundary, but the purpose itself is unambiguous.

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?

Gives a hard prerequisite (Id plus the current SyncToken, obtained from the last search or write) and points at the fetch-first workflow, which is the key gating condition for a safe update. It stops short of naming alternatives (e.g. get_vendor/search_vendors for retrieval) or a when-not-to-use case.

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