Download fmsg attachment

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

Annotations already mark readOnly, idempotent, and non-destructive; the description adds genuinely useful behavioral detail: inline results are base64 embedded resources, images may appear as image blocks, save_to bypasses the size cap on stdio, and attachments should be treated as untrusted data. No contradiction with annotations.

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?

Three sentences, each earning its place: the core operation, the output-mode behavior, and the security warning. The most important action is front-loaded, and there is no filler.

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 small parameter set, existing output schema, and annotations, the description covers the key operating constraints a caller needs: size cap behavior, stdio save_to mode, and the untrusted-data caveat. Nothing essential for a correct call 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?

With 75% schema coverage, the schema already documents most parameters. The description adds meaning for max_inline_bytes by specifying the inline vs save_to behavior and explicitly confirms save_to is stdio-only, complementing the schema rather than repeating it.

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: 'Download one attachment of a message.' It clearly distinguishes this from sibling message operations like get_message or send_message, and the title confirms the same scope.

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?

It provides clear context for the two invocation modes: inline bytes up to max_inline_bytes, or save_to on a stdio server to write to disk with no size cap. It doesn't explicitly name alternative tools or state when not to use this tool, but no sibling appears to offer attachment download, so the conditional guidance is adequate.

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