Download a media item

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

Annotations already cover readOnly, idempotent, and non-destructive. The description adds meaningful behavioral details: it resolves the item's current base_url internally, works with a plain id, and never relies on a stale URL. It also discloses the return type (base64 + mime), going beyond what annotations express. No contradiction detected.

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 concise, purposeful sentences. The first frontloads the action and output format; the second explains the URL-resolution behavior and its benefit. No filler or repetition of schema fields.

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 simple download tool with four documented parameters, no output schema, and a safety profile in annotations, the description covers the essential return information (base64 + mime), the scoping limitation (this app uploaded), and the id handling behavior. It does not detail error or size-limit behavior, but max_mb is already documented in the schema.

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 baseline is 3. The description adds value by specifying that media_item_id should be a plain id (not a pre-resolved URL) and that the tool handles resolution itself, which the schema's 'The media item to download.' does not convey.

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 ('Fetch') and resource ('bytes of a media item this app uploaded'), and clarifies that output is base64 with mime type. This clearly distinguishes it from siblings like get_media_item, which likely returns metadata rather than raw bytes.

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 implies the right context — using a plain media_item_id for an app-uploaded item when raw bytes are needed. However, it never explicitly contrasts with related siblings such as download_picked or get_media_item, so an agent gets no direct 'when-not-to-use' guidance.

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