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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds that the URL is 'signed' and returns an 'upload_token', implying credential minting, plus the possibility of a validation error — useful context, but no expiry, permission, or side-effect details beyond that.

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 short sentences, purpose front-loaded before the return details. Enumerating file_id, file_url, upload_url and upload_token is mildly redundant given the output schema, but it is compact and wastes little space.

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 an output schema covering return values and annotations covering the safety profile, the description only needs to establish purpose and workflow position. It establishes purpose but omits where this step sits relative to upload_media, leaving the agent to infer the upload sequence on its own.

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 file_name, file_size and content_type are already fully documented in the schema, including the default of 0 for file_size. The description adds no format, constraint, or size-limit information on top of that, so the baseline 3 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?

Names a specific verb and resource: creating a signed upload URL for a media file. The scope ('selected in the upload UI') is concrete and helps separate it from the sibling upload_media, though the relationship to that sibling is never stated explicitly.

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?

Usage is only implied by the phrase 'a media file selected in the upload UI', which hints this is a preparatory step in a UI flow. There is no explicit when-to-use statement, no exclusions, and no reference to the upload_media sibling that presumably performs the actual transfer.

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