Add text overlays

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

The description goes beyond annotations by explaining the sidecar file mechanism, which guarantees character safety, and notes that everything renders in one pass. These are behavioral traits that the annotations (all false) do not convey. It does not fully describe output handling, but the schema covers output_path, so the description adds substantial context.

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?

The description is compact and front-loaded, with a clear first sentence stating purpose. The subsequent sentences efficiently add feature details and the sidecar safety note without fluff. Every sentence earns its place, making the description easy to scan.

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 tool with a complex schema, the description covers the essential behavior, item structure, and a notable edge case (special characters). An output schema exists, so not describing return values is acceptable. The only gap is explicit usage guidance, which is already partial, but overall the description is sufficient for an agent to invoke the tool correctly.

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 description adds meaning to the 'items' parameter by explaining each item's timing, position, font, and animation, which complements the schema's per-field descriptions. It also clarifies the safety of any text via the sidecar note. Given 50% schema coverage, the description compensates well by summarizing the core structure, though it does not detail encode options, which are already self-described in the schema.

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 opens with a specific verb and resource: 'Draw titles and lower-thirds over the video, with timing and animation.' This clearly distinguishes it from siblings like burn_captions (caption burning) and overlay_media (media overlay), as it focuses on text overlays with timing and animation.

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 implies usage by describing the tool's purpose and features, but it does not explicitly state when to use this tool versus alternatives like burn_captions or overlay_media. There is no when-to-use or when-not-to-use guidance, leaving the agent to infer the appropriate context.

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