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

Annotations already declare readOnly, idempotent, non-destructive, openWorld, so the safety profile is covered. The description adds two non-obvious behaviors an agent would otherwise guess wrong: cached copies carry freshness metadata, and reading does not mark the message as read — the latter being especially valuable given mark_email_read exists as a sibling.

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, no filler, and the core verb+identifier is front-loaded before the caching and side-effect notes. Each sentence carries distinct information.

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 and 4 parameters, the description covers the return shape at a high level ('message body and attachment metadata'), the caching/freshness contract, and the read-state side effect. It leaves error behavior and where the opaque ID comes from unstated, which is a minor but real gap.

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 coverage is 50%: waitForFresh and maxWaitMs are documented in-schema, while accountId and messageId are not. The description compensates partially, telling the agent that messageId is 'opaque' (so it cannot be constructed) and framing waitForFresh as a 'bounded' refresh, but says nothing about accountId.

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 a specific verb and resource ('Read a message body and attachment metadata') and constrains retrieval to an 'opaque message ID', which separates it from browse-style siblings like search_emails and get_thread. It stops short of naming an alternative tool, so differentiation is implied rather than explicit.

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?

It gives a clear conditional instruction for the refresh path ('set waitForFresh for a bounded provider refresh'), which tells the agent when to opt into the slower behavior. It does not say when to prefer this tool over get_thread or search_emails, so routing among siblings is left to inference.

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