Read Message Body

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds the useful scoping note that the message_id must already be known, but it says nothing about truncation via max_body_chars or the 304 conditional-fetch behavior exposed in the schema.

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?

Two tight sentences with the purpose stated first and the selection preference second; no filler, no repetition of the title.

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 shape need not be described, and the read-only annotations carry most behavioral weight. The definition is nearly sufficient for this simple read, with only the relationship to the full-message sibling and truncation behavior left implicit.

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 coverage is 100%, so every parameter including part, mailbox_id, max_body_chars and If-None-Match is already documented in the schema. The description's phrase "raw or simplified body" loosely gestures at the part enum but adds no format or truncation semantics beyond what the schema states, so the baseline 3 applies.

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 uses a specific verb ("read") and resource ("the raw or simplified body for a known message_id"), so the agent knows exactly what is fetched. It differentiates itself indirectly from the heavier message-fetch sibling by saying it is for cases that don't need "every MIME detail," but it never names that 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?

"Use this to read ... Prefer it when the task needs message text but not every MIME detail" gives a clear positive condition for selection. What is missing is an explicit pointer to the alternative tool (e.g. mailbox_get_message) that should be used when full MIME structure is required.

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