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

Annotations already declare readOnlyHint=false, idempotentHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely new behavior: it will POST event JSON to the URL with an HMAC-SHA256 signature, plus the plan-entitlement requirement. It omits whether a signing secret is returned at creation or how duplicate URLs are handled.

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 short sentences, front-loaded with what the tool does, then delivery semantics, then the plan gate. No filler or redundancy; 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 5-parameter create tool with full schema coverage and standard annotations, the description covers purpose, delivery mechanism and entitlement. The notable gap is that with no output schema, it doesn't say what is returned on success (e.g. a webhook id or signing secret), which the agent would need for follow-up calls.

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 five parameters (url, name, apiKey, events, enabled) are already documented in the schema. The description only refers obliquely to the URL and event payload and adds no field-level meaning beyond the schema; 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?

Names a specific verb and resource: 'Register an outgoing webhook endpoint.' An agent can immediately distinguish this from create_contact, create_campaign and other create_* siblings. It stops short of a 5 only because it never names a sibling (e.g. list_webhooks, regenerate_webhook_secret) to contrast against.

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 guidance on when to create a webhook versus using automations or other event mechanisms, and no alternatives are referenced. The one eligibility note ('outgoing webhooks are a plan feature') is a constraint rather than usage direction, and it is buried at the end.

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