get_attachment

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

The description adds concrete non-obvious behavior beyond the annotations: the 25 MB decoded size barrier, that images come back as image resources while other files are returned as base64 in structured output, and that returned data should be treated as potentially malicious. This is valuable behavioral context not present in readOnlyHint or idempotentHint.

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?

The description is compact: three sentences, each carrying a distinct job – purpose, behavior/output, and alternative/security. It is front-loaded and contains no repetitive or obituary content.

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?

Together with a fully-explained input schema, an output schema, and annotations, the description covers what the tool does, the size limits, the output modes, and the alternative when not to use it. It is complete enough for an agent to call the tool without guessing.

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% and each required parameter already has a helpful sentence (e.g., index comes from list_attachments or get_email, uidvalidity detects stale uids). The description itself adds no direct parameter-level semantics, 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?

States a specific action and resource ('Fetch one attachment's content'), a concrete scope ('one attachment', 'up to 25 MB decoded'), and enough detail to distinguish it from siblings such as list_attachments and save_attachment. The behavior is not ambiguous or tautological.

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?

Explicitly gives a when-not-to-use condition and alternative: 'For an attachment too large to be worth reading inline, use save_attachment instead.' This gives the agent a clear choosing heuristic, and the rest implies it should be used for inline retrieval when the size is acceptable.

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