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

Annotations declare the tool is not read-only and not idempotent, but the description adds valuable context: the endpoint must be public and HTTPS, and the signing secret is returned only once. This clarifies side effects (secret not retrievable later) beyond what annotations provide.

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?

A single, well-structured sentence that front-loads the action and includes the key return behavior. No wasted words; every phrase earns its place.

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 one-parameter tool, the description covers purpose, key constraints (public HTTPS), and the critical return value (signing secret once). It does not mention error conditions or idempotency implications, but annotations already convey idempotency as false, so the description is adequately complete.

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 schema only defines 'url' with length constraints. The description adds crucial semantic meaning: the URL must be a public HTTPS endpoint, which is not evident from the schema. This significantly improves parameter understanding despite 0% schema coverage.

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 verb ('Opt in') and resource ('signed event delivery to a public HTTPS endpoint'), clearly indicating the tool creates a webhook. It also distinguishes itself from related siblings like revoke_webhook and get_webhook_deliveries by its focus on creation and the one-time secret return.

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 implies usage for setting up event delivery but does not explicitly state when to use it versus alternatives. It lacks exclusion criteria or reference to sibling tools, leaving the agent to infer based on the name and context.

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