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

Annotations already flag destructiveHint=true and readOnlyHint=false, so the mutation/destructive nature is covered. The description adds the SyncToken requirement, which hints at stale-token/optimistic-locking behavior, but it does not disclose the sparse-update semantics or full-update clearing behavior itself; those live in the parameter schema rather than the tool description.

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?

The description is a single front-loaded sentence with no filler: subject, action, resource, and the essential precondition all appear in order. Every word earns its place.

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?

Together with the rich entity schema, the tool gives an agent enough to invoke it correctly: prerequisite fields, sparse behavior, line-replacement caveat, sensitive-field restrictions, and company disambiguation. The only notable omission is an explicit statement of the response/return value, but with no output schema and a straightforward update operation that gap is minor.

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%, and the entity parameter description already details Id/SyncToken requirements, sparse updates, Line-array replacement, and forbidden sensitive fields. The top-level description's 'requires Id and SyncToken' restates that schema content, adding no new parameter-level 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?

The description states a specific verb and resource ('Update an existing attachable in QuickBooks Online') and adds a key prerequisite, so an agent knows what the tool acts on. It implies the attachable must already exist, which loosely separates it from create_attachable and delete_attachable, though it does not name those siblings explicitly.

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 clear precondition: the attachable must already exist and the call requires Id and SyncToken. However, it never states when to prefer create_attachable/delete_attachable, what happens with a stale SyncToken, or any exclusion, so an agent must infer the boundary between update and create/delete.

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