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

Adds substantial behavior beyond the annotations (which only say non-read-only, non-idempotent, open-world): the 45 s wait before falling back to a job_id, credit charging, plan quality caps, and an authentication requirement with a host sign-in prompt. These are exactly the operational facts an agent needs and cannot get from structured fields.

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 compact passage, front-loaded with the operation and its output, then the cost/limit, then the async fallback and the auth prerequisite. Every clause carries information; nothing is padding.

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 an output schema present, return values need no explanation, and the description covers cost, limits, async behavior and auth. Minor gap: it does not say what happens if the job is still pending or how the job_id should be consumed beyond naming get_job.

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 80%, so the schema already documents image sources, scale, context, llm_model and conversation_id. The description reiterates the allowed scales and the image source types but adds no syntax or format detail beyond that, so the baseline 3 applies.

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), the accepted resource types (StockCake images or your own edited images), the exact multiplier set (2x/4x/8x) and the output format (lossless PNG). This is clearly distinguishable from the sibling 'resize_image' purely on the verb, 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 real operating conditions: plan quality caps apply and credits are charged otherwise, and it names the follow-up tool (get_job) for the async path. It stops short of an explicit when-to-use-this-versus-resize_image or generate_image rule, so it is clear context rather than full routing guidance.

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