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

Despite annotations already covering read-only/idempotent safety, the description adds substantial behavioral detail: draft/outbox inclusion, conditional availability of body_text and attachments based on access level, body truncation flagging, and a prompt-injection warning about treating body content as data. This is exactly the kind of context annotations cannot convey.

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?

The description is front-loaded with the core operation, then layers access, truncation, and prompt-injection guidance in tight, purposeful sentences. Every sentence earns its place, with no filler or repetition.

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 return-value explanation is not needed. The description covers the conditional return behavior (access level, truncation) and operational caveats that matter for a single-email read, making it complete for the tool's complexity.

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 single `id` parameter is fully documented in the schema. The description reinforces that the ID can reference synced, sent, draft, or outbox mail, but adds no syntax or format detail beyond what the schema provides.

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 opens with a precise verb+resource: 'Read one email by ID.' It immediately scopes the resource to synced mail, sent mail, and the user's own drafts/outbox emails, which distinguishes this single-item read from the list-emails-tool sibling.

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 clear: read a single email when you have its ID, and the schema points to the list emails tool as the ID source. There is no explicit when-not-to-use or named alternative beyond the implicit single-vs-list distinction, so it falls just short of a 5.

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