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

Annotations cover the side-effect profile (write, open-world, non-idempotent), and the description goes well beyond them by disclosing the billing consequence, approximate latency, output format, and the concrete handle it returns for chaining. Nothing contradicts the annotations and no relevant trait is hidden.

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?

A single front-loaded sentence: purpose first, then output/handle, then cost, latency, and endpoint. Every clause carries actionable information and there is no filler.

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?

With no output schema, the description correctly explains the return (a visible image plus its mediaId) and how to use it downstream. Together with the annotations and fully documented schema, an agent has everything needed to invoke this correctly.

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 100%, so the baseline is 3; the description earns an extra point by mapping the aspectRatio enum to actual pixel dimensions (1376x768 / 1024x1024 / 768x1376) and by quantifying the style set. It slightly misstates the style count (7 entries in the enum include "none", the default), but otherwise adds meaning over the schema.

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 and resource ("Generate one JPEG ... from a prompt") and pins down scope with the three supported resolutions and existence of styles. It also distinguishes itself from siblings by naming the downstream artifacts (startImage / referenceImage_N / avatar picture), which separates it from vids_create_avatar and vids_create_video.

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?

Gives clear context for when this is the right call (you need a generated still to feed a video or avatar) and warns of the cost (one image from the monthly allowance) and latency (~10 s). It never names an alternative for the case where the user already has an image (e.g. vids_upload_asset), so exclusions are absent.

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