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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so 'Read-only' is largely redundant. However, since there is no output schema, the statement that results include URLs, events and status genuinely tells the agent what comes back, and the note about limit/page support sets expectations for paged results.

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, with the scope and the sibling disambiguation front-loaded before the read-only/pagination note. No filler or repetition.

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 zero-required-parameter list tool with rich annotations and full schema coverage, the description covers purpose, the sibling boundary, and the returned fields. Minor gaps remain around pagination metadata (total counts, page size limits), but nothing critical to invoking it 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 'page' and 'limit' are already documented in the schema. The description merely restates that limit and page are supported without adding defaults, maximums, or paging semantics, so 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 gives a specific verb and resource ('List webhooks for transactional (Email API) mail') and explicitly disambiguates from the sibling list_webhooks, which handles campaign webhooks. An agent can distinguish this from list_webhooks and get_webhook without opening a 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 (list_webhooks) and the condition that selects it (campaign webhooks), which is the key routing decision for this tool. It doesn't describe scenarios for calling it, such as auditing before toggle_transactional_webhook, so it stops short of full when/when-not guidance.

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