Read an email

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

The description discloses that the body is HTML converted to plain text by default, that attachment metadata excludes file contents, and that it is read-only. Annotations already mark readOnlyHint=true, so the description adds valuable detail beyond what annotations provide. No contradictions.

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 a single, well-structured sentence that clearly states the tool's purpose and key behaviors without extraneous words. Information about attachments is appended concisely. Every sentence earns its place.

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 read tool with two parameters and no output schema, the description covers the input requirement, the parameter options, the return fields, and important limitations (no file contents). It is complete given the tool's simplicity and the presence of annotations.

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?

Both parameters are fully described in the input schema (100% coverage). The description mentions 'by id' and the format parameter's default, but does not add significant meaning beyond the schema's descriptions. Baseline 3 is appropriate.

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 the action ('Read a single email message by id'), specifies the return fields (subject, sender, etc.), and distinguishes from sibling tools like list_messages which does not return the full body. The verb 'Read' and resource 'email message' are specific and unambiguous.

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 this tool (when you need full details of one message) and provides context through the 'format' parameter hint. However, it does not explicitly state when not to use it or mention alternatives like list_messages for overviews, though the sibling context makes this clear.

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