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

Annotations already establish that this is a non-read-only, non-destructive operation. The description adds real behavioral context beyond them: it opens a UI panel, the upload is performed from the browser, and the resulting file URL is posted into the chat. It does not mention auth or size limits, but the added interaction detail is valuable.

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 sentences, front-loaded with the core purpose followed by mechanism and usage condition. Mostly efficient, though the final clause 'including files attached to the chat' is grammatically awkward and slightly obscures its meaning.

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 zero-parameter widget tool with no output schema, the description covers what happens (panel opens, browser-side upload, URL posted to chat) and when to use it. It is nearly complete, missing only an explicit pointer to the sibling 'upload_file' alternative.

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 and the schema is trivially complete, so there is nothing for the description to disambiguate. The 0-parameter baseline of 4 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?

The description states a specific action and mechanism: it 'opens a panel where the user can pick a local file to upload to their workspace' and posts the URL into the chat. This clearly conveys a distinct interaction model, though it does not explicitly name or contrast with the sibling 'upload_file'.

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 gives a concrete condition for use: 'For clients that cannot send HTTP requests.' This is a clear when-to-use signal that implicitly distinguishes it from an HTTP-based upload path, but it never names the alternative tool explicitly, so it falls short of full routing guidance.

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