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

Annotations already flag destructive=true, readOnly=false, non-idempotent and open-world, but the description adds what the annotations cannot: the settings gate, credential class required, the preview-vs-send branch on confirm, and that every send is logged. This is exactly the extra context an agent needs for an irreversible send.

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?

Purpose is front-loaded in the first clause, followed by prerequisites and the preview/logging behavior. The middle sentence packs many conditions into one long chain, which is dense but every clause carries a real invocation constraint, so nothing should be cut.

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 mutation tool with no output schema, the description covers the gating conditions, the no-op preview path, and the audit log. It stops short of describing failure modes (what an error looks like when the setting is off or the allowance is exhausted), a minor gap given the otherwise thorough coverage.

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% and each of the three params is documented in the schema, including confirm's preview semantics. The description restates confirm behavior rather than adding format or edge-case meaning beyond it, 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 specific verb and resource ('Send an existing reply draft') and ties it to the sibling that produces the input ('from draft_email_reply'), so the agent can distinguish it from draft_email_reply and get_email without opening either schema.

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?

Explicit preconditions: farm OWNER must have enabled 'Allow AI assistant to send' (off by default), owner/admin read/write AI keys only, confirm: true required, and daily send allowance must remain. It also names the preview path when confirm is absent, so when-to-use and when-not-to-send are both spelled out.

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