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

Annotations already declare destructiveHint=true, openWorldHint=true, idempotentHint=false, so the agent knows this is an outward-facing, irreversible write. The description adds the human-authorization gate, which is real value beyond annotations, but the phrase 'Connecting is not sending approval' is cryptic and no delivery/quota/rate-limit behavior is 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?

Two short, front-loaded sentences with zero padding – the purpose comes first and the authorization caveat second. The second sentence is terse to the point of ambiguity, which slightly weakens otherwise tight structure.

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?

An output schema exists and parameter documentation is thorough, so the remaining burden is routing and behavioral context. With 11 parameters and four sibling mail-composition tools, the description should clarify the reply-vs-send boundary and idempotency expectations, which it does not.

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 91%, so the schema already documents nearly every parameter, including in_reply_to semantics and idempotency_key retention rules. The description adds no parameter-level detail, 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?

States a clear verb+resource ('Send an email or reply') with the payload described as 'recipients and content'. However, it does not distinguish itself from the several sibling tools that also compose mail (reply_message, reply_all_message, send_draft, forward_message), so the agent must infer the boundary.

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 sentence 'authorized by the human' and 'Connecting is not sending approval' implies a precondition (explicit human authorization to send) but never states when to prefer this tool over reply_message or send_draft, nor when not to use it. Usage is implied, not spelled out.

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