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

With no annotations provided, the description carries the behavioral disclosure burden. It does well by explaining that bodies are fetched on demand and cached, that this call can be slower than list calls, and that attachment contents are never returned. It does not describe the response shape, but the core behavior is well covered.

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 three sentences with no filler. The primary purpose is front-loaded, followed by two caveats that each earn their place: the performance/caching behavior and the attachment exclusion. Every sentence contributes to correct invocation.

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 single-parameter tool with no output schema, the description is largely complete: it states what is returned (full body), the key limitation (no attachment contents), and the triggering condition (snippet insufficient). A brief note on the return format would make it fully complete, but nothing essential for invoking the tool is missing.

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%, with messageId already described as 'Message id from email_get_thread.' The tool description adds little parameter-level meaning beyond reinforcing that it refers to a single email message, so the schema does the heavy lifting and the baseline of 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 opens with a specific verb and resource: 'Read the full body of ONE email message.' It clearly distinguishes this from the sibling list tools by emphasizing it handles a single message rather than a list, and the 'snippet' contrast implies the full content that list/thread tools truncate.

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 gives an explicit when-to-use rule: 'ask for it only when a snippet is not enough to answer the question.' It also points to the alternative category ('the list calls') and sets performance expectations, so an agent knows this is a targeted follow-up call rather than the default listing operation.

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