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

Annotations already declare readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false, so the safety profile is covered. The description adds genuinely useful behavior — an outbound HTTPS POST fired when mail arrives — but says nothing about duplicate registrations, whether a signing secret is issued, or whether the endpoint must be verified first.

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?

A single front-loaded sentence carrying the verb, the artifact created, and the trigger condition, with zero filler. Nothing in it is redundant with the title.

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 4-parameter mutation tool with no output schema, the definition covers what is created and what fires it, which is enough to call it correctly. The remaining gap — no mention of the created resource's identifier or secret — is modest and partially inferred from the required parameters.

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 coverage is 75%: url, orgId and agentId are documented, but `eventTypes` has no schema description. The description implies the notification event (mail arrival) yet does not enumerate accepted event-type values, so it fails to compensate for the one undocumented parameter.

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?

Specific verb ('Registers') plus resource ('an HTTPS URL') plus scope ('organization's inboxes'), so the agent knows exactly what is created and what triggers it. However, it never distinguishes itself from the sibling `webhook_create`, which appears to be the non-organization variant, leaving the agent to infer which one applies.

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 phrase 'at one of the organization's inboxes' implicitly scopes this to org-level, inbox-scoped webhooks, which hints at the split from `webhook_create`, but there is no explicit when-to-use statement or exclusion. No prerequisites (auth/role, URL verification, limits) are mentioned.

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