Generate video posters

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

Annotations declare readOnlyHint=false and openWorldHint=true, marking this as a write operation. The description adds the crucial async behavior (results must be polled rather than returned inline) and the input constraint (public video URL), which annotations do not convey. It omits auth/permission requirements and any rate-limit 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?

Two tight sentences, front-loaded with purpose and followed by the required follow-up action. Every clause earns its place with no redundancy.

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 single-parameter async job creator with no output schema, the description covers the essentials: what it makes, from what input, and how to retrieve results. Explicit mention of the returned job identifier or how to match it to a poll call would complete it.

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 must carry the burden. It adds real meaning by specifying the URL must point to a public video, but it does not explain the nested 'data' wrapper or format expectations beyond the schema's uri type.

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?

States a specific verb ('Generate'), a clear resource ('poster (thumbnail) images'), and the input scope ('from a public video URL'). It also names the sibling get_poster_job, letting an agent distinguish the creator from the poller without opening either schema.

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?

Explicitly tells the agent the follow-up workflow: poll reddit_ads_get_poster_job for the result, which is the key usage instruction for an async job. It lacks explicit when-not-to-use guidance versus alternatives like upload_creative_assets, so it falls short of a 5.

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