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

Annotations already declare readOnly/idempotent/non-destructive, so the bar is lower, yet the description adds substantial context: GOVERNED behavior where only allowlisted senders are ever scanned, plus the exact return shapes {status:'found', code, from, message_id} or {status:'not_found'} in the absence of an output schema, and the required `read` capability. This is genuinely useful behavioral disclosure beyond structured fields.

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 tight sentences, front-loaded with the core action and code format, followed by the governance constraint and return shape. No wasted clauses.

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 compensates by specifying return fields and both status outcomes, and it covers the security-relevant allowlist constraint and capability requirement. An agent has everything needed to call it correctly.

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%, so the schema already documents `from`, `inbox_id`, and `max_age_minutes`. The description only loosely reinforces these ('recent mail', 'scoped inbox', 'expected code sender') without adding syntax or format detail beyond the schema. 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 precise verb+resource: 'Extract a one-time / verification code (a 4–8 digit number) from recent mail in a scoped inbox.' The narrowed scope (code extraction, not general message retrieval) clearly distinguishes it from siblings like mailbuttons_get_message or mailbuttons_list_messages.

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 usage context (recent mail, scoped inbox, allowlisted senders) and the `max_age_minutes` framing suggests freshness matters, but it never explicitly says when to choose this over mailbuttons_get_message or get_thread, nor does it state exclusions. Guidance is implied rather than stated.

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