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

Annotations already declare destructiveHint=true, idempotentHint=true and openWorldHint=false, so most of the 'Safety' sentence restates structured data. The one genuinely additive point is that previous values are not automatically preserved or restored, which tells the agent there is no undo path, plus the account-scoping note. Useful but largely duplicative.

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 with the purpose front-loaded and the safety caveat second, which is the right ordering for a mutation tool. The 'Safety:' label is slightly boilerplate and could be folded into a single clause.

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?

An output schema exists and the input schema is fully described, so the description needn't explain return values. Given the tool's complexity (nested object parameter, destructive overwrite semantics), the description covers scope and irreversibility adequately, though it omits update semantics for omitted fields.

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 every parameter including the nested `data` object is already documented with examples (color as hex without '#', name such as 'Golf Clubs'). The description adds nothing about parameter behavior, merge order, or which fields are mutable, 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?

The first sentence gives a specific verb ('Update'), a specific resource ('custom activity category'), and a scope ('owned by the authenticated user by id'), which separates it from the create/delete/list/show siblings in the categories family. It stops short of naming an alternative tool or clarifying when a partial update is preferable to a full overwrite, so it lands just below the top mark.

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?

There is no explicit when-to-use or when-not-to-use guidance and no mention of the siblings (e.g. categories_show to read current values before overwriting, or categories_delete for removal). The only implied usage is 'by id', leaving the agent to infer prerequisites and alternatives entirely.

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