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

With no annotations supplied, the description carries the full burden and does meaningful work: it discloses that a signing secret is generated and returned only once, that HMAC verification is the intended use, and that the endpoint is global rather than per-product. It still omits duplicate-URL behavior, required permissions, and whether registration triggers an immediate test delivery.

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 the action and immediately followed by the highest-value caveat (one-time secret). No filler, though the scope sentence could be folded in more tightly.

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 two-parameter mutation with no annotations and no output schema, the description covers the essentials an agent needs: what is registered, what comes back (a one-time signing secret), and the event scope. Remaining gaps are the undocumented 'description' parameter and the exact shape of the response.

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 50%: 'url' is documented as an HTTPS callback on the merchant's server, which the description only restates, and the 'description' parameter is undocumented in both schema and description. The description adds no meaning beyond the schema for either 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?

States a specific verb and resource ('Register a webhook URL') and clarifies scope with 'Not per-product — one endpoint receives all paid events', which distinguishes it from any per-product webhook concept. It stops short of naming the sibling tools (list_merchant_webhooks, send_merchant_webhook_test) that an agent might otherwise confuse it with.

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?

Usage is implied by the scope sentence: register this when the merchant wants to receive all paid events at a single endpoint. However, there is no explicit when-to-use/when-not-to-use guidance, no prerequisite (e.g. HTTPS requirement is only in the schema), and no pointer to send_merchant_webhook_test for verification or list_merchant_webhooks for existing registrations.

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