Gemini video understanding

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered without description. The description adds meaningful behavior: the tool accepts exactly one video source and never reclassifies the caller-selected modality, which is a non-obvious quirk beyond the annotations. It does not contradict any annotation.

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 sentences, front-loaded with the core purpose, and each clause contributes either input constraints or the no-reclassification caveat. There is no filler or redundant restatement of the schema.

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 three-parameter tool with rich schema descriptions and safe-read annotations, the description covers input modes and the key behavioral quirk. It does not describe the return format, but no output schema exists and the prompt schema implies a text-based Gemini response, so the missing piece is minor.

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 coverage is 100%, but the description still adds value by specifying that 'source' can be a public YouTube URL, a direct remote video URL, or a local video path, and by clarifying that the caller controls the modality. This enriches the generic 'public HTTP(S) URL' schema text and reinforces prompt/mimeType intent.

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 uses a specific verb+resource ('Understand one video source') and enumerates accepted source types (YouTube URL, direct remote video URL, local video path), which clearly maps to the video modality among siblings. It does not explicitly contrast with sibling tools, but the resource type and tool title make the purpose unambiguous.

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?

The description states valid input forms and warns that the caller must choose the modality because the server will not reclassify the source, giving some context on source selection. It does not explicitly say when to prefer this tool over web/audio/document/image siblings, so usage guidance is implied rather than explicit.

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