download_attachment

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

With no annotations provided, the description carries the behavioral disclosure burden, and it does so well: it reveals the base64-encoded return format, instructs the agent to decode it, and warns that the content can be large. It does not cover failure modes or rate limits, but for a simple read operation the key behaviors are disclosed.

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 compact sentences deliver the core action, return format, decoding step, size caveat, and usage guidance. There is no redundant or filler content, and the most important information is front-loaded.

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 two-parameter tool with fully described schema fields, the description covers everything an agent needs to select and invoke it correctly: the operation, the output encoding, the size risk, and the alternative to use for metadata-only checks.

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%, so the schema already fully documents both id and index. The description adds only marginal parameter context by referencing the attachments array, but it does not materially extend what the schema already provides.

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 from a message.' It clearly distinguishes this tool from sibling get_message by noting that get_message's attachments array already provides metadata, making the tool's unique purpose obvious.

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 states when to prefer this tool—'only when the file content is actually needed'—and when not to use it (just checking existence), pointing to get_message as the lighter-weight alternative. This gives the agent clear decision criteria.

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