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

Annotations already cover the safety profile (readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false), and the description layers on real behavioral facts: the signing secret is returned ONCE, activation requires a signed challenge echo, no customer contact fields are transmitted, and OAuth scopes are required. None of this duplicates the annotations, and 'changes buyer or order state' reinforces the mutation semantics consistently.

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?

Purpose is front-loaded in the first sentence and every subsequent clause carries distinct operational value (secret handling, activation, privacy, scopes, state change). It is slightly telegraphic — 'Check expires_at and requires_active_grant' reads as a note fragment rather than a sentence — but there is no padding.

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?

An output schema exists, yet the description still surfaces the two facts an agent most needs from the response (one-time secret, activation gating via expires_at/requires_active_grant) plus auth scope requirements and the privacy guarantee. For a mutation tool with side effects on buyer/order state, nothing essential to correct invocation 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% and both parameters are fully documented in-schema (HTTPS pattern, private-network rejection, event enum meanings). The description's 'public HTTPS receiver' phrasing reinforces callback_url but adds no format, constraint, or default information beyond what the schema already carries, 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?

States a specific verb and resource — 'Create a pending order event subscription to a public HTTPS receiver' — and immediately differentiates from the read-side siblings (list_webhooks, delete_webhook) by framing it as a pending/activation-gated creation. An agent knows exactly what object is being produced without opening the 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?

Prerequisites are explicit: public HTTPS receiver, must echo the signed challenge before activation, and required OAuth scopes (webhooks:write, orders:read) are named. It also tells the agent to inspect expires_at and requires_active_grant. It stops short of naming when NOT to use this vs. an alternative create path, so it falls just below the top band.

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