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

Annotations declare destructiveHint: true, so the tool has potential side effects. The description adds a useful behavioral note about attachment handling (original attachments not included by default), which goes beyond annotations. However, it doesn't mention the non-idempotent nature (idempotentHint false) or clarify what the destructive aspect entails, so it provides modest extra context.

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?

Two sentences, zero filler. The core purpose is front-loaded, and the key caveat about attachments is stated immediately after. Every word earns its place, making it efficient and easy to parse.

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 an output schema exists and the schema fully describes all parameters, the description is largely complete for a forward operation. It covers the main behavioral nuance (attachment handling) not obvious from the schema. However, it does not mention the requirement of at least one recipient (though schema covers it) or the idempotency/retry implications, but those are structured fields. Overall, it's sufficiently complete for the tool's 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?

Schema description coverage is 100%, providing a baseline of 3. The description adds extra meaning by explaining that original attachments are excluded unless selected or the original .eml is attached, which directly clarifies the relationship between attachmentIds and attachOriginal parameters beyond their individual schema descriptions. This enriches parameter understanding, justifying a step above baseline.

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 states a clear verb ('Forward') and resource (email to recipients), distinguishing it from reply_email and send_email by the explicit recipient specification. However, it does not explicitly name the original message context (via messageId) or a sibling alternative, so it's clear but not perfectly differentiated.

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?

No guidance on when to use this tool versus siblings like reply_email or send_email. The description only states what it does, not when it's the appropriate choice or what differentiates it. Without explicit or implied usage context, an agent may invoke it incorrectly.

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