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

Annotations declare destructiveHint=true and readOnlyHint=false, and the description adds genuinely non-annotated behavior: optimistic concurrency via SyncToken, the requirement to fetch the current token, and that the recorded return carries a new token. It stops short of describing what an update destroys (the sparse-vs-full clear semantics live only in the schema), which is the main remaining behavioral gap.

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 tight sentences with zero filler; the prerequisite is front-loaded and the return-value note follows. Nothing redundant is included.

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, the description usefully states what is returned (the saved record with its new SyncToken), and it covers the required concurrency token. It is only slightly short of complete because the destructive sparse/full-update consequence — flagged by destructiveHint=true — is not surfaced in the description itself.

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 documents both the entity payload (including Id/SyncToken and sparse semantics) and the company selector. The description only restates the Id/SyncToken requirement, adding no syntax or format detail beyond structured fields — the baseline 3 for full coverage 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 ("Update an existing attachable in QuickBooks Online") and adds the key concurrency prerequisite. It distinguishes itself from create_attachable/get_attachable by the word "existing", though it never names those siblings explicitly, so an agent must infer the routing.

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 prerequisite chain is implied well — "the current SyncToken, as the last search or write returned it" tells the agent to read the record first, which points implicitly at get_attachable/search_attachables. However, there is no explicit when-to-use vs. create_attachable or delete_attachable, and no guidance on when an update is preferable to recreating the record.

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