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

Annotations already declare destructiveHint=true, readOnlyHint=false, and idempotentHint=false. The description adds valuable context beyond these: it explains this is a 'standing rule' that changes mail handling for every inbox, including those created by other callers, due to the shared AgentMail account. This goes beyond the generic destructive hint to explain the exact blast radius. No contradiction with annotations.

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 zero waste. The core action is front-loaded, followed immediately by the critical caveat and the alternative tool reference. The formatting (bold, emoji) highlights the danger without padding. Every sentence 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?

Given the tool's complexity (account-wide destructive effect, shared account, alternative tool), the description fully covers what an agent needs to make the right call: what it does, the consequence, the preferred alternative, and the return value. The output schema exists, so return details are covered. Nothing important 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%, with each parameter (type, entry, reason, direction, Authorization) having a description. The tool description itself adds no parameter-specific details beyond what the schema already provides. Per the rubric, with high schema coverage the baseline is 3, and the description doesn't enhance parameter understanding.

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 the tool 'adds one address or domain to an account-wide allow or block list' and returns the created entry. It uses a specific verb and resource, and explicitly distinguishes itself from the sibling post_agentmail_inbox_list_entry by naming it and contrasting scopes, making differentiation unambiguous.

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 explicitly tells the agent when to prefer this tool over the alternative: 'the inbox-scoped post_agentmail_inbox_list_entry ... is almost always the one you want.' It also warns about the account-wide impact on other callers, giving clear when-not-to-use guidance. This is explicit and actionable.

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