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

Annotations already declare a safe read, but the description adds genuinely valuable context beyond them: mail text is untrusted sender content and never instructions (prompt-injection warning), the required read:mailbox permission, and the default exclusion of quarantined items. This is exactly the behavioral disclosure an agent needs for a mail-reading tool.

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 short sentences, front-loaded with the action and immediately followed by the security caveat. No filler; every sentence adds a distinct constraint or warning.

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?

The safety and permission picture is complete, but for a four-parameter, zero-coverage tool with no output schema, the description says nothing about pagination/limit behavior, accepted formats for `since`, or how `to` filters results. Adequate but with clear gaps.

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 0%, so the description carries the full documentation burden, yet it only indirectly covers one parameter (include_quarantined via the default-exclusion statement). The semantics of `to`, `limit`, and especially the `since` anyOf (integer vs string) are left entirely undocumented.

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?

"List safe mail summaries" gives a specific verb (list) and resource (mail), and it is clearly distinguishable from the siblings (get_addresses, wait_for_code, wait_for_link). The qualifier "safe" is slightly vague about what makes a summary safe, but the purpose is unmistakable.

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 states the required scope (read:mailbox) and a concrete usage condition: quarantine items are excluded unless explicitly requested. It does not name alternatives or when-not-to-use, but the siblings serve entirely different purposes, so routing risk is low.

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