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

Annotations already declare readOnly/idempotent/non-destructive, but the description earns credit for adding non-structural behavior: the required email:read scope, the guarantee that credentials are never returned, that no setup or permissions are mutated, and the consent boundary (setup never authorizes a draft). That is exactly the kind of context annotations cannot express.

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?

Front-loaded with the action and use context, then auth scope, return payload, and consent boundaries. Tight overall, though the closing 'Changes no setup or permissions' and 'Setup never authorizes a draft' overlap slightly, costing a small amount of redundancy.

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?

With no output schema, the description carries the return burden itself and does so by listing the exact fields returned. Combined with the auth scope and the explicit statement that nothing is mutated, an agent has everything needed to call this safely.

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 tool takes zero parameters, so the baseline of 4 applies; there is nothing further the description could meaningfully add on parameter usage. No parameter-level semantics are needed or missing.

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 ('Check outgoing-mail setup') and immediately enumerates what it returns (per-mailbox outgoing enabled status, fixed From address, agent_send_authorized, setup_url). This is clearly distinguishable from write-side siblings like prepare_email_draft and send_email.

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?

Gives an explicit trigger ('before offering to prepare a reply or new email') and draws the boundary against alternatives: reading/monitoring do not require sending, while preparing or sending drafts needs separate email:send consent. Nothing is left to inference about when this tool applies versus its siblings.

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