reply_to_email

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

The description adds useful behavioral context: sender address and threading headers are derived from the original message. However, the statement 'only the body is required' is slightly misleading because email_id is a required parameter. It does not contradict 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?

Two sentences, front-loaded with the action. The second sentence is efficient but introduces a minor ambiguity around required parameters, preventing a perfect score.

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?

For a simple mutation tool with only three parameters and no output schema, the description covers purpose and the key derivation behavior. It is sufficiently complete, though it could clarify the required email_id and what outcome to expect.

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 coverage is 100% with good parameter descriptions. The description adds marginal conceptual context about the body being the main content, but does not significantly expand on 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 clearly states the tool's verb ('Reply') and resource ('existing email thread'), and distinguishes it from send_email by noting threading headers are derived from the original. This makes the tool's purpose unambiguous and differentiates it from siblings.

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 implies when to use the tool (replying to an existing thread) and provides context that only the body is needed, but it does not explicitly name alternatives or state when not to use it. The sibling context (send_email) provides implicit differentiation.

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