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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=true, so the safety profile is covered. The description adds the HTTPS/public-host requirement and the dry-run validation path, but does not disclose what happens if a webhook with the same URL already exists (relevant given idempotentHint=false), whether verification is required before events flow, or what the create call returns.

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 purpose and event scope, then routing guidance, then the dry-run escape hatch. Nothing is redundant and every clause carries information.

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 four-parameter create tool with annotations and no output schema, the description covers purpose, required inputs, sibling routing and a validation mode. The only meaningful gap is the absence of any indication of the return value (e.g., the created webhook id) or post-creation verification, which the description would need to supply since no output schema exists.

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 each of the four parameters is already documented inline, including the event enum. The description only restates the required trio ('Needs name, an https url and events') and the dry_run meaning, adding little beyond the schema — the baseline 3 applies.

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 opens with a specific verb and resource ('Create a webhook that receives transactional (Email API) events') and enumerates the exact event stream, which immediately separates it from the campaign-webhook sibling. An agent can tell this apart from create_webhook without inspecting either schema.

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 names the alternative explicitly ('For campaign events use create_webhook') and states the condition that selects it, plus a second usage mode ('Set dry_run: true to validate without creating'). Both the when and the when-not are spelled out rather than inferred.

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