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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the operation's safety is covered. The description adds meaningful context beyond annotations by explaining that these are control-plane records and that realtime traffic flows directly Unipile -> destination, not through Nilyo. This clarifies the nature of the data returned and the architectural role of the destinations, which is valuable for the agent.

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?

The description is two sentences with no wasted words. The action and scope are front-loaded ('List webhook destinations created by this Nilyo user'), and the second sentence adds essential context about control-plane vs. data-plane. Every sentence earns its place, and it is highly concise.

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 simple list tool with no parameters, no output schema, and comprehensive annotations (readOnly, idempotent, non-destructive), the description is mostly complete. It specifies the scope (created by this user) and clarifies the architectural role of the records. However, it does not mention what fields are returned or whether pagination is involved, though without an output schema, the agent might need such hints. Still, for a zero-parameter list, the description is adequate and goes beyond minimal requirements.

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?

The tool has zero parameters, so schema coverage is trivially 100%. The description does not need to explain any parameters, and the baseline for 0 params is 4. The description adds no parameter-specific semantics because none exist, which is appropriate.

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 clearly states a specific verb (list) and resource (webhook destinations created by this Nilyo user), and the scope is explicit. It distinguishes itself from siblings like webhook_get_destination (which retrieves a single record) by implying a listing operation, and the mention of 'created by this Nilyo user' adds precision.

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 description provides context about control-plane records but does not explicitly state when to use this tool versus alternatives like webhook_get_destination or webhook_list_available_events. The usage is implied (when you need all destinations for the user), but no direct comparison or exclusion is given. Given the simplicity of the tool (no parameters), this is a moderate gap, not a severe one.

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