fetch_message

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

Annotations already cover readOnly/idempotent/non-destructive/openWorld, so the description correctly spends its budget elsewhere: it discloses page-concatenation semantics, the source_sha256 cross-page invariant, and that a partial page is not a complete message. It also flags email text as untrusted data and never instructions, a meaningful prompt-injection warning. It stops short of describing error behavior or what a completed fetch returns structurally.

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?

Five terse, front-loaded sentences with no filler; the core action leads and the safety warning sits last where it will still be read. Every sentence adds operational information.

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 4-parameter tool with no output schema and no per-parameter documentation, the description is adequate but incomplete. It covers the pagination/JSON contract and the untrusted-data stance well, yet leaves the required message_ref identifier and the meaning of limit/offset entirely unexplained.

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%, so the description must carry the load. It maps the four section values (headers/text/html/attachments) to the enum and implies pagination via limit/offset ('concatenate paginated untrusted_data'), but message_ref, limit, and offset are never explained, and no format or range guidance is added.

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?

States a specific verb and resource ('Fetch complete message sections') and enumerates the four selectable sections, which maps directly onto the section enum. It is distinct from fetch_attachment and search_messages, though it never names those siblings explicitly to sharpen the distinction.

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 explains how to fetch (EXAMINE, BODY.PEEK, section choice) but never states when to use this tool versus search_messages or fetch_attachment. No prerequisites, no when-not conditions, no alternative routing are given; usage must be inferred from the name.

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