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

Goes well beyond the annotations by disclosing the environment-dependent behavior (widget only appears in MCP Apps hosts; otherwise nothing renders and local files must go through the public API, with a docs link), and that it returns a sessionId whose uploaded files surface in conversation or via uploadWidgetStatusTool. That is exactly the non-obvious operational context annotations cannot carry.

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?

Front-loaded with the action and the routing rule, then the environment caveat and return note. Slightly redundant at the tail: 'uploadFromUrlTool is only for public URLs' restates the routing already given in sentence two.

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 explains the key return value (sessionId) and how the actual uploaded files reach the user, plus the host-app fallback path. Nothing an agent needs in order to call it and handle the result correctly 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate; baseline applies. The description does not clutter the call signature with irrelevant instructions, which is correct for a no-arg tool.

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 ('Show the user an upload widget to add images or videos from their own device to the media library'), and explicitly separates itself from uploadFromUrlTool and from the status tool. An agent can distinguish it from every upload-related sibling without opening a 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?

Gives an explicit trigger ('when the user wants to attach a local file to a post'), an explicit exclusion with the named alternative ('when the media is already available on a public URL, use uploadFromUrlTool instead'), and an environment precondition for when the widget is even available.

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