Open a pre-filled compose window

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

The description discloses the critical limitation (no ability to send email), the deliberate UI behavior, the instruction to inform the user, and the return shape. Annotations are all false and do not contradict; the description adds significant behavioral context beyond them.

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 three short paragraphs: function, limitation plus user guidance, and return shape. Every sentence earns its place with no filler or unnecessary 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?

With no output schema, the description provides the return object shape. It also clarifies the no-send behavior, which is essential for safe use. Combined with complete schema coverage, this is fully adequate for a tool of this complexity.

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?

All 5 parameters already have schema descriptions (100% coverage). The description only echoes recipients/subject/body in prose without adding format or constraint details beyond what the schema already provides, so 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: 'Open a new compose window in Mail.app pre-filled with recipients, subject and body.' This clearly distinguishes the tool from sibling list/search/get tools by being the only compose action.

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 clearly states when to use the tool and what to expect: it cannot send email, leaves the window open for the user to review and send by hand, and says to mention this to the user. It provides strong usage context but does not explicitly name alternative sibling tools.

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