reels_preview

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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered by structured data. The description contributes the return medium ("inline image"), which matters because there is no output schema, but it says nothing about cost, latency, resolution, or whether repeated renders are cached.

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 short sentences, zero filler, with the core action front-loaded before the parameter hints. Every clause carries distinct information.

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 3-parameter, no-output-schema tool, the definition covers the output form and two of three parameters, which is decent. It still leaves projectId's role unexplained and gives no hint about what the returned frame's size or format will be, nor how it differs from reels_preview_asset.

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 0%, so the description carries the full burden and does add meaning: "sparse key times" explains that the time parameter should be sampled sparingly, and "enable guides" explains what the guides flag surfaces (safe-zone overlays). Only projectId is left unaddressed, which keeps it out of the top score.

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 sentence "Render one frame as an inline image" gives a specific verb (render), a specific unit of output (one frame), and the result form (inline image). It is clearly narrower than reels_render or reels_render_status, though it never explicitly contrasts itself with the similarly named sibling reels_preview_asset, so the differentiation is implied rather than stated.

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?

"Use sparse key times" and "enable guides to inspect safe zones" give real invocation advice for two of the parameters, which is more than most definitions offer. However, there is no guidance on when to choose this over reels_preview_asset or a full reels_render, and no stated exclusions or prerequisites.

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