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

Annotations only declare it is a non-read-only, non-idempotent, open-world, non-destructive write. The description adds substantial behavior beyond that: the signing secret is returned only once, delivery is at-least-once with bounded retries, unsafe destinations are refused, and there is a five-receiver quota.

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?

Four dense sentences, front-loaded with purpose and auth/return semantics before delivery behavior and quota. Every sentence carries information, though the HMAC-verification sentence is receiver-side guidance rather than this tool's action.

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 and only one parameter, the description still covers the return value (signing secret, once), authentication scope, delivery guarantees, and failure/quota limits. An agent has everything needed to call it and to anticipate the outcome.

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 single url parameter is already documented in the schema, including the no-redirect/no-private-address rule. The description's 'public HTTPS receiver' phrasing reinforces rather than extends the schema, 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 states a specific verb (Register) and resource (public HTTPS receiver for signed lifecycle events), plus the scope (this organization). It is trivially distinguishable from revoke_webhook and get_webhook_deliveries, which are the related siblings.

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 states prerequisites (webhooks scope), hard constraints (public HTTPS only, no redirects, no private-network resolution, max five active receivers), which tells the agent when this call will fail. It does not explicitly name alternatives or say when not to register at all, but the operational context is clear.

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