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

With no annotations, the description carries the full disclosure burden. It explains that the original message context is included, that a note can be prepended, and that the subject is auto-prefixed with 'Fwd:'. It does not cover permissions, rate limits, or failure behavior, but for a forwarding operation, these key behaviors are well disclosed.

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?

Three short sentences, front-loaded with the core action, and each sentence adds value. The API endpoint is useful for technical integration, and there is no redundant text.

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?

The tool has 5 parameters, all documented, and no output schema. The description explains the forwarding behavior, the inclusion of original context, and the optional note, which is sufficient for an agent to correctly invoke the tool. It does not mention return values, but for a straightforward forward operation this is not a critical gap.

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 input schema covers all parameter descriptions (100% coverage), so baseline is 3. The description adds meaningful context beyond the schema: it explains the 'text' parameter as an optional note to prepend, and the auto-prefix behavior clarifies why there is no subject parameter. This enriches the schema.

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 uses a specific verb ('Forward') with a clear resource ('an email message to another address'). It also distinguishes from siblings like send_email or reply_to_message by noting it includes original message context and auto-prefixes subject with 'Fwd:'.

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 implies the tool is for forwarding emails, but it does not explicitly mention when to use this instead of alternatives like reply_to_message or send_email. The context is clear enough for an agent to infer, but there is no explicit when/when-not guidance.

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