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

Beyond the annotations (readOnlyHint=false, openWorldHint=true), the description discloses several behavioral traits an agent could not infer: the signing secret is returned once and never again, the payload carries counts and a link but not the places themselves, and it requires an API key plus a paid plan while consuming no credits.

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?

It is front-loaded and every sentence carries information, but the conversational phrasing ("Tell us where to POST", "instead of asking us every few seconds") is more colorful than strictly necessary for a specification.

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 no output schema, the description correctly covers the return surface (the one-time signing secret), along with auth requirements, plan gating, cost, and payload shape. Nothing material for 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%, so url, events, and description are already fully documented, setting the baseline at 3. The description adds payload/secret context but no additional per-parameter syntax or format meaning.

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 states a specific action and resource: registering a URL where events are POSTed when a collection ends. It is clear what the tool creates, though it relies on the title ("Add a webhook endpoint") and never names itself relative to siblings like update_webhook or delete_webhook.

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 gives a clear rationale for using this over polling ("instead of asking us every few seconds whether it is done"), which is strong when-to-use context. It does not, however, distinguish itself from sibling webhook tools such as test_webhook or update_webhook.

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