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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the mutating nature of the tool is known. The description adds useful behavioral context by stating that the endpoint and watched resource cannot change, which is a non-obvious constraint beyond the schema. It does not contradict any annotation.

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 two sentences with no filler. The core operation is front-loaded, and the important limitation plus alternative is provided in the second sentence. 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?

For a tool with a complete input schema, an output schema, and annotations covering safety hints, the description fully covers what an agent needs: what the tool updates, what it cannot update, and what to do instead. Nothing critical is missing for correct invocation.

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 all four parameters are already documented in the input schema. The description does not add substantial parameter-level detail beyond saying 'event list', but it does clarify that enabledEvents is a full replacement rather than an incremental update. This matches the schema's 'Full replacement' wording, so the value added beyond the schema is minimal.

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 names a specific operation — replacing a webhook subscription's event list — and clearly scopes it to the webhooks group. It also distinguishes itself from the sibling create_webhook_subscription and delete_webhook_subscription tools by noting that endpoint and watched resource cannot change. This is unambiguous and differentiates the tool from related update tools in the sibling list.

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 description explicitly states when this tool is appropriate (replacing the event list) and when it is not (changing the endpoint or watched resource), and gives the alternative: delete and recreate the subscription. This is direct, actionable guidance that prevents an agent from attempting an unsupported update.

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