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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering safety and side-effect profile. The description adds the return content (metadata and body), which is useful but not beyond what annotations already imply. No additional behavioral context like error handling or rate limits is provided, but this is a simple read operation where the annotations do most of the work.

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 two sentences with zero waste. The primary function is front-loaded, and the alternative usage is stated in a separate clause. Every word earns its place, making it efficient and clear.

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?

Given the output schema exists, the description does not need to explain return values. The tool is simple with one parameter, and the description covers purpose and guidance. It does not mention potential error scenarios or how to obtain the ID, but these are minor for a straightforward getter. Overall, it is sufficient for an agent to 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?

The schema description for the 'id' parameter already states 'Email ID. Returns full metadata and body.', which fully covers the semantics. The tool description repeats this but adds no new information. Given 100% schema coverage, the baseline of 3 is appropriate; the description does not enhance parameter understanding.

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 verb 'Fetch' and the resource 'full detail for a single email by ID', specifying the content (metadata and body). It also differentiates itself from email_list by naming it as the browsing tool, which is a sibling. This makes the purpose unambiguous and distinguishes it from related tools.

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 explicitly directs the agent to 'Use email_list to browse emails in a folder', which is a clear alternative for a related task. However, it does not cover other potential alternatives like email_search or email_thread_get, but for its specific role (fetching a single email by ID) the guidance is sufficient.

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