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

Beyond the readOnly and idempotent annotations, the description adds meaningful behavior: it will not mark the email as read, returns bounded plain text, and explicitly instructs the agent to ignore email-embedded instructions and never follow links or exfiltrate content. This is valuable security-relevant context that the annotations do not provide.

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 compact and front-loaded: the core behavior is in the first sentence, and the safety warning is in the second. Every clause adds information, and there is no redundant or filler content.

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?

For a simple two-parameter, read-only tool, the description covers the main behavior, side-effect avoidance, and a critical security caveat. However, since there is no output schema, the description does not fully specify what the returned plain-text representation includes or how it is structured, leaving a minor completeness 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 description coverage is 0%, and the description does not explain mailboxId or messageId beyond the phrase 'one email.' The parameter names are fairly self-explanatory, which prevents a score of 1, but the description adds no substantive meaning about how these IDs relate to mailboxes or which values are expected.

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 clearly states a specific verb, resource, and qualifiers: 'Read one email as bounded plain text without marking it read.' It differentiates this from sibling tools like search_messages or get_draft by focusing on a single email read operation. The behavior is unambiguous and actionable.

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 implies when to use the tool: when you need to read one specific email without side effects. However, it does not explicitly mention alternatives or exclusion criteria, such as using get_draft for drafts or search_messages for discovery. The usage context is clear but left to inference.

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