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

Annotations already declare readOnly, idempotent and non-destructive, so the safety bar is met structurally. The description adds genuinely useful context - newest-first ordering, default coverage of both directions, and 'Free' (no credit cost) - but says nothing about pagination, result volume or what a message record contains.

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?

It is short and front-loads the resource and ordering, but the trailing 'Free. Free.' is a duplicated token that adds no information and reads as an editing artifact.

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?

There is no output schema, so the description should ideally sketch the return shape and note default limits (limit defaults to 25, max 100), neither of which appears. For an 8-parameter list tool with low schema coverage, this is adequate but has 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?

With only 38% schema coverage across 8 parameters, the description compensates partially by explaining inbox, from, since and direction (in/out). It leaves query, limit, label and state unmentioned, so half the surface is undocumented in the description on top of thin schema text.

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?

The description names the resource (messages in this account's inboxes) and the scope (received, sent or both, newest first), which lets an agent distinguish it from email_get_message and email_get_thread by granularity. It doesn't explicitly name those siblings, keeping it below a 5.

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?

Usage is implied through the filter list ('optionally for one inbox, one sender or since a time'), but it never says when to reach for this versus email_list_inboxes or email_get_thread, and gives no exclusions or prerequisites.

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