get_attachment

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open world), so the bar is lower. The description adds two things annotations cannot: a 5 MB size ceiling and an explicit prompt-injection warning that returned content is untrusted data and never instructions. The return encoding/pagination behavior is not described, but the security-relevant context is the more valuable disclosure here.

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 sentences, no filler. The action and size limit come first, and the untrusted-content warning is placed last as a distinct safety caveat. Every clause earns its place.

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 3-parameter, no-output-schema tool the description covers purpose, provenance of the key parameter, and a hard limit. It omits what the agent actually receives (raw bytes vs. base64 vs. a reference) and what happens when the 5 MB limit is exceeded, which are the only meaningful remaining gaps.

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%; each of account, messageId, and partId is already documented in the schema, including the partId format example. The description reinforces partId provenance but adds no syntax or constraint detail beyond the schema. 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?

States a specific verb and resource (download one attachment), identifies the exact source of the required partId (get_message or get_thread), and adds a concrete size boundary. It is plainly distinguishable from all siblings, none of which fetch attachment bodies.

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 tells the agent where partId comes from, which implies the correct call sequence (fetch message/thread first, then this tool). It does not state exclusions or what to do if the attachment exceeds 5 MB, so it stops short of full when/when-not guidance, but for a tool with no competing sibling the routing context is clear.

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