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

Annotations already declare non-readonly, non-idempotent, non-destructive, closed-world behavior, so the baseline bar is lower. The description adds useful delivery semantics (an outbound POST on event fire) but says nothing about persistence, retries, signing/verification, or the fact that repeated create calls produce duplicate subscriptions (consistent with idempotentHint=false).

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 short sentences with the use case stated first and the mechanism second; nothing is padding. The conversational 'when you want ppl to notify you' phrasing is slightly casual for a tool definition but not wasteful.

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 an output schema present, full schema coverage, and annotations carrying the safety profile, the description only needs to convey purpose and the POST-on-event behavior — which it does. Nothing required to call it correctly is missing.

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 url, events, and approval_id are already fully documented in the schema, including the comma-separated event format and 'omit for all events'. The description's event examples (contact created, birthday, task due) hint at event names but add no syntax or constraints beyond the schema, so 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 description gives a concrete mechanism: hand the service a URL and it will POST to it when an event fires, contrasted with polling. That's a specific action and resource, distinguishable from webhooks.list and webhooks.delete. It never explicitly says 'creates a persistent subscription,' leaving that to the title, which keeps it from a 5.

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 supplies a real selection criterion — use this when you want real-time notification instead of polling — and illustrates trigger cases (contact created, birthday, task due). It does not state exclusions or point at siblings like webhooks.list for inspection, so no 5.

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