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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds a concrete inventory of what comes back (body, attachment names, folder, classification), which is useful scoping context, but says nothing about failure modes (invalid/deleted id) or size limits on the body.

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?

A single compact sentence, front-loaded with the core capability and then the field inventory. Nothing is wasted, though the fragmentary phrasing (no verb) is slightly less scannable than a full clause.

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?

An output schema exists, so the return value explanation is largely redundant here, and annotations cover read-only semantics. What is missing is positioning relative to search_emails — the one thing an agent needs to sequence the call 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 coverage is 100% and the single `id` parameter already documents its source ("as returned by search_emails or list_to_answer"). The description adds no parameter-level detail of its own, so the baseline of 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?

"One email in full" plus an enumeration of returned fields makes clear this retrieves a single complete message, which is distinct from search_emails/list_to_answer among the siblings. It stops short of an explicit verb+resource statement ("retrieve an email by id"), so it is clear but not maximally sharp.

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?

There is no guidance on when to call this versus search_emails, list_to_answer, or the mutation siblings like move_email/archive_email. The agent must infer that this is the full-body read step after a search, with no stated prerequisites or exclusions.

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