meta_ads_videos_thumbnails

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

With no annotations provided, the description carries the full burden and does so well. It explicitly states 'Read-only — does not modify the account,' and also discloses a behavioral nuance: 'Thumbnails only exist once processing has finished, so check meta_ads_videos_get first — an empty list usually means the video is still processing.' This provides critical operational context beyond the raw schema.

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 three concise sentences, each serving a distinct purpose: stating the function, listing return fields, and giving usage guidance. It is front-loaded with the core purpose and avoids redundancy, earning a top score.

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?

Since no output schema exists, the description compensates by explicitly enumerating the return fields (id, uri, is_preferred, height, width). It also covers prerequisites (video processing completion) and the next step in the workflow (passing uri to meta_ads_creatives_create), making the tool fully understandable in its operational context.

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 input schema already provides descriptions for both parameters (video_id and account_id) with 100% coverage, so the description adds little beyond what the schema states. It does not elaborate on parameter semantics further, making the baseline 3 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 opens with 'Lists the thumbnails Meta auto-generated for an uploaded video,' which clearly specifies the verb ('Lists') and the resource ('thumbnails' for a video). It also differentiates from sibling tools like meta_ads_videos_get by focusing specifically on thumbnail generation and returning fields (id, uri, is_preferred, height, width).

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 provides explicit guidance on when to use the tool: after uploading a video, and it advises checking meta_ads_videos_get first to ensure processing is complete. It also explains how to use the result (pick preferred thumbnail and pass its uri to meta_ads_creatives_create), giving both context and a concrete downstream action.

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