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

With no annotations present, the description carries the burden well: it discloses the credit cost per resolution (2/3/5), that the operation is asynchronous and must be polled via wait_for_image, and that it renders a live preview in app-capable hosts. It does not cover failure behavior or how long polling typically takes, which is the remaining gap.

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?

Four short sentences, each carrying unique payload (capability, cost, input sourcing, polling), with the core purpose front-loaded. No filler or repetition of the tool name.

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 and no annotations, the description supplies cost, async/polling behavior, input provenance, and host preview support, which is nearly everything needed to invoke it correctly. Minor omissions (failure modes, expected wait time) keep it from a 5.

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, but the description adds real meaning: imageUrl is constrained to public URLs sourced from generation outputUrl or upload_file, and resolution choices are tied to specific credit costs. That is value beyond the schema's terse field descriptions.

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 (upscale) and resource (image) with an explicit range of outputs (2K/4K/8K) and names the product surface (Image Upscaler). An agent can immediately separate it from the sibling upscale_video 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?

Gives the workflow context an agent needs: the input must be a public URL, either a generation outputUrl or an upload_file url, and results are polled with wait_for_image. No explicit when-not-to-use or alternative routing (e.g., vs. create_image) is given, so it stops 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.