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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds genuinely useful behavior beyond that: secrets are never returned, and a sub-account key sees only endpoints scoped to exactly its own sub-account — a non-obvious visibility rule that affects result interpretation.

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 core sentence is front-loaded and dense with useful detail, and the security/scoping caveats follow logically. The ACCESS block is slightly verbose and its 'start_login does NOT open this tool' phrasing is awkward, but it carries necessary authentication 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?

An output schema exists, so return values need not be described, and the description still names the key fields. Authentication requirements and the sub-account visibility rule are both covered; only the sibling-routing guidance 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline 4 applies. The description correctly implies no filtering arguments are needed.

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+resource ('List the account's webhook endpoints') and enumerates the fields returned (URL, events, scope, sub-accounts, status), so the agent knows exactly what it gets. It does not explicitly distinguish itself from get_webhook_endpoint or list_webhook_deliveries, which keeps it from a 5.

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 context is implied by the plural 'list' and the sub-account scoping note, and the ACCESS paragraph tells the agent it must authenticate first. However, there is no explicit guidance on when to prefer this over get_webhook_endpoint (single endpoint) or list_webhook_deliveries (delivery history), so the agent must infer the boundary.

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