List Mail accounts

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is known. The description adds behavioral context by specifying the return structure including `mail_running` boolean, which signals whether Mail.app is running, and the detailed account object fields, providing value beyond the 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 highly concise: three short sentences that each serve a distinct purpose (what it does, when to use it, what it returns). It is front-loaded with the core action and avoids any 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?

This is a simple list tool with rich annotations and an output schema. The description provides the essential return format and usage context, making it fully self-contained for an agent to select and invoke correctly. The guidance about other tools taking names verbatim completes the contextual picture.

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 has zero parameters, and the schema coverage is 100% (effectively no schema to document). Per the guidelines, a baseline of 4 is appropriate. The description does not need to explain parameters because there are none, and it does not introduce any ambiguity.

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 'List every email account configured in macOS Mail.app' with a specific verb and resource. It also distinguishes itself from siblings by noting that other tools take account names verbatim, positioning this as the entry point.

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 says 'Start here when you do not yet know the exact account names — every other tool takes those names verbatim.' This gives clear when-to-use guidance and implies that alternatives require the output of this tool, even though no specific sibling is named.

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