Render a frame to look at

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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds valuable behavioral context beyond annotations: the PNG has a transparent background because comp background color is a preview setting and never renders, and it advises adding a solid layer for an opaque backdrop. This is exactly the kind of non-obvious behavior an agent needs to know. It doesn't mention performance or file size implications, but the transparency disclosure is significant.

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 two short paragraphs, front-loaded with the core action and purpose. Every sentence earns its place: the first sentence states what it does, the second explains when to use it, and the third paragraph discloses a critical behavioral gotcha. No fluff or repetition.

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 read-only preview tool with 100% schema coverage and no output schema, the description is nearly complete. It covers the core action, the use case, and the transparent-background gotcha. It could mention that the returned image is what the agent will see (i.e., the response contains the image), but the returnImage parameter and the phrase 'return it as an image' already imply that. The only minor gap is not explaining what happens if the comp is missing or the time is invalid, but that's not essential for a read-only tool.

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 all 5 parameters. The description adds context about the default behavior (returning an image) and the transparent background, but doesn't add much per-parameter meaning beyond what the schema provides. Baseline 3 is appropriate.

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 states a specific verb ('Render a single frame... to PNG and return it as an image') and resource ('a composition'), and clearly distinguishes it from the sibling ae_render by emphasizing single-frame preview and visual checking. It also explains the purpose ('so you can see what the comp actually looks like'), which helps an agent understand when to use it.

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 explicitly says to use this tool to check work after making changes and warns not to assume an edit landed as intended. It also provides a clear exclusion/alternative context by contrasting with rendering a full composition (sibling ae_render), and gives practical guidance about transparent backgrounds. This is strong usage guidance.

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