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

The description adds substantial behavior beyond the annotations: the payload is HMAC-signed with a returned secret that is shown only once (an undeniably important, irreversible consequence), identical requests are deduplicated for 24 hours, and idempotency-key reuse semantics are spelled out. This goes well past idempotentHint/openWorldHint and gives the agent what it needs to warn about the one-time secret.

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 dense sentences, front-loaded with the action, then the security/dedup caveats. The 'Step 10: Get told about calls' opener is the only soft sentence, reading as workflow narration rather than tool 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?

For a mutating, open-world creation tool with no output schema, the description covers the essentials: what is created, which events, the one-time secret, and dedup behavior. It stops short of describing the response body or what happens on an invalid/unreachable URL, but nothing critical 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?

With only 50% schema description coverage, the description must compensate: it enumerates the allowed event types and explains the idempotencyKey repeat-vs-retry distinction. It says nothing about URL constraints (e.g., must be a reachable HTTPS endpoint) or that businessId defaults to the API key's business, leaving half the surface to the schema alone.

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 concrete verb and resource: 'Subscribe a URL to call.completed / message.taken / balance.low events,' which clearly marks this as webhook creation and separates it from ringkit_list_webhooks. The 'Step 10: Get told about calls' lead-in is onboarding-flavored rather than a clean statement of purpose, but the substantive sentence is unambiguous.

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 through the 'Step 10' framing and the note that a new idempotencyKey should be used 'only to deliberately repeat the action,' which is real guidance on a parameter. However, the description never says when to create a webhook versus querying existing ones with ringkit_list_webhooks, nor does it state prerequisites such as needing a valid business or verified endpoint.

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