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

Annotations cover the safety profile (destructiveHint=true, readOnlyHint=false), so the bar is lower. The description still adds real value by disclosing the optimistic-concurrency requirement (Id + current SyncToken) and the return behavior (saved record with new SyncToken), which are not in the annotations.

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 tightly written sentences with zero waste, front-loading the action and immediately following with the key prerequisite and return value.

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 correctly notes the return value ('saved record with its new SyncToken'), and the SyncToken concurrency workflow is explained. The nested entity object is fully covered by the schema, so the definition is essentially complete, missing only explicit guidance on sibling selection.

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 and company parameters, including sparse-update semantics. The description restates the Id/SyncToken requirement but adds no syntax or format detail beyond what the schema provides; 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 ('time activity') with product context ('QuickBooks Online'), clearly distinguishing it from create_time_activity, delete_time_activity, get_time_activity, and search_time_activities. It does not explicitly name those siblings, but the verb+resource 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?

The requirement to supply the current SyncToken 'as the last search or write returned it' implies the agent must first fetch the record (via get_time_activity or search_time_activities), which is useful workflow guidance. However, it never explicitly states when to prefer this tool over alternatives or what preconditions apply beyond the token.

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