Get an attachment

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

Beyond the readOnly/idempotent/non-destructive annotations, it discloses decryption of encrypted-room uploads, integrity verification against the uploader's SHA-256, per-type size thresholds, the side effect of writing to the private data directory, and the ephemeral-mode exception where nothing is written to disk. This is exactly the extra behavioral context annotations cannot express.

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 core action is front-loaded and every clause carries information — type-based return behavior, size limits, disk-write policy, and identifier sourcing. It is one dense paragraph rather than scannable bullets, but there is essentially 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?

With no output schema, the description carries the return-value burden and does so fully: text for text-like files, images under 4 MiB, a file path for other files, or an inline binary resource in ephemeral mode. An agent has everything needed to call and interpret the result.

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 coverage is 100%, so the baseline is 3, but the description adds real meaning: file_id and message_id are presented as alternative identifying routes, and max_inline_bytes is tied specifically to the text-like-file threshold. It doesn't document the default value or bounds for max_inline_bytes, which remain schema-only.

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 states a specific verb and resource ('Download an attachment and decrypt it locally'), and the mechanics (decrypt encrypted rooms, SHA-256 integrity check) make it unmistakable against siblings like get_message or get_user. An agent can tell exactly what this returns (text, image, or a saved path) without opening the schema.

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 how to source the identifiers — 'file_id (from a message's attachments) or by message_id' — which is genuine usage context. It does not state when to prefer this over get_message or otherwise route between alternatives, so no explicit exclusions are provided.

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