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

With annotations already declaring read-only, idempotent, non-destructive behavior, the description adds useful rendering behavior beyond the annotations: media frame numbering, transparency checkerboard display, full-size limits, and inline images plus signed download URLs. It does not discuss authentication, errors, or rate limits, but it covers the core behavioral traits an agent needs.

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 a single dense paragraph with the main action front-loaded and no obvious filler. It is appropriately sized for the tool’s complexity, though some semicolon-heavy clauses reduce readability slightly.

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?

Given an output schema and safety annotations, the description covers purpose, frame limits, layout behavior, transparency handling, output formats, and delivery mechanism. The main remaining gap is the absence of any explanation for long_edge, and the timeline/media exclusivity is only implied.

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 high at 88%, establishing a baseline of 3, and the description adds meaningful semantics: the 16-frame cap, grid versus single layout, full-size limited to 4 frames at original media size, format/quality behavior, and media-frame numbering. It does not address the long_edge parameter, which appears to be the schema’s undocumented parameter.

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 clearly states that it renders up to 16 frame images from a timeline or media file, either as one contact-sheet grid or as individual images. It is specific about the output form and limits, but it does not explicitly name or differentiate itself from sibling tools such as export.video or create.still.

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 clear usage context: look at a timeline or media file, use grid for a contact sheet, single for individual images, and size full for thumbnails and stills to keep. It does not state when not to use it or name alternative tools, so it stops short of explicit routing guidance.

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