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

Annotations already declare the safety profile (readOnlyHint=false, openWorldHint=true, destructiveHint=true), so the description earns credit for adding context beyond them: it identifies this as a 'state-changing external action' and states it operates only on the owned subscription 'after authorization', implying an ownership/permission gate. It does not explain the destructive semantics — e.g. whether the events array or metadata object wholesale replaces existing values — which is the main remaining 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?

Three sentences, front-loaded with the trigger condition, then the state-changing nature, then prerequisites. No filler, no restatement of the tool name, and each sentence carries distinct information.

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 five-parameter mutation tool with no output schema, the description covers trigger, mutation intent, authorization/ownership and prerequisite lookup tools. The missing piece is update semantics — whether omitted fields are preserved and whether nested values (events, metadata) are replaced — which matters given the nested object and the destructiveHint.

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 all five parameters and the baseline is 3. The description goes beyond that by specifying the provenance of two parameters ('subscription_id from list-webhook-subscriptions', 'valid keys' via list-webhook-events), which is real routing value the schema does not carry.

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 gives a specific verb ('updates the owned webhook subscription') and enumerates exactly which fields can change (endpoint URL, subscribed events, active/inactive status, metadata), which lets an agent separate this from create-webhook-subscription, delete-webhook-subscription and list-webhook-subscriptions without opening any schema.

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 opens with an explicit trigger ('Use this when the user wants to change ...') and routes the agent to the prerequisite tools for subscription_id and event keys. It stops short of a when-not statement or naming the adjacent create/delete siblings as alternatives, so it is strong but not fully exhaustive guidance.

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