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

Annotations only declare the non-read-only, non-idempotent, non-destructive profile, so the description adds real value: it explains that this is an interactive widget, that the chosen media IDs come back in the conversation, and that an upload_url exists for browser-based clients. It omits permission/auth requirements and any note on what happens if the user cancels the widget.

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?

Three tight sentences with no filler; the core action is front-loaded and the fallback mechanism is placed last, in the order an agent would need it.

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?

An output schema exists, yet the description still usefully characterizes the return payload (media IDs, upload_url), and it covers the interaction model, the fallback path, and the file scope. Nothing an agent needs to decide and invoke this zero-parameter widget tool is missing.

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?

Zero parameters, so there is nothing for the description to disambiguate and the baseline of 4 applies. No parameter noise is introduced.

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 ('Shows an upload widget where the user picks images or videos... into the media library') and adds the discriminating condition 'for files without a public URL', which separates it from upload_media/upload_media_file/create_media_upload_ticket without naming them. An agent can tell what this tool does and roughly who it's for from the first sentence.

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?

Gives two clear use conditions: files lacking a public URL, and clients that cannot render widgets (use the upload_url fallback). It stops short of explicitly naming alternative siblings such as upload_media_file, so the agent must infer the routing rather than being told it outright.

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