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

Annotations cover the safety profile (not read-only, not idempotent, not destructive), so the description's added value is the blocking/wait-until-processed behavior and the 'small file' size constraint, which are real traits beyond structured data. It stops short of stating exact size limits, auth requirements, or failure behavior, keeping it out of 5 territory.

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, front-loaded with the action and constraint, followed by the return shape and the routing to the alternative. Every sentence carries distinct information with no redundancy.

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 present, return values need not be re-explained, yet the description usefully summarizes the id and signed URLs. Combined with full schema coverage and clear sibling routing, nothing an agent needs to invoke this 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?

Schema description coverage is 100%, so the schema already documents fileData, type (with enum), and displayName. The description restates that contents are base64-encoded but adds no syntax, format, or default details beyond what the schema provides, matching the baseline when the schema does the heavy lifting.

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 (upload) and resource (file) with scope qualifiers ('small file... base64-encoded contents'), and explicitly distinguishes itself from the sibling create_file_upload for large files. An agent can identify the tool and its domain without opening the 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?

Names the alternative explicitly ('For large files, use create_file_upload instead') with the condition that selects it, and enumerates downstream consumers (voiceover_to_video, slideshow_to_video, logos, B-roll) so the agent knows where the returned fileId feeds. When-to-use and when-not-to-use are both present.

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