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

Annotations only declare the generic write/open-world/non-idempotent profile; the description goes well beyond them by disclosing that the call spends account balance, that billing varies per image/megapixel/token, where the charge surfaces (usage_get), and that the image is returned synchronously as content. No contradiction with readOnlyHint=false or destructiveHint=false.

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?

Front-loaded with purpose and return behavior, then model eligibility and the size limit, then cost. Three short paragraphs, each carrying non-redundant information, though the billing sentence is somewhat dense and could be trimmed without loss.

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?

No output schema exists, but the description states what comes back (image content immediately), covers cost implications, model eligibility, and size caveats — everything an agent needs to invoke this correctly. Nothing material is left to inference.

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 adds real meaning on top by explaining the size tiers ("4K can be heavier than your client accepts" → prefer 2K) and by constraining the model parameter to ids whose tool is "image_generate". The n multiplier's per-image billing is also flagged, though the schema already covers it.

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 opening sentence names a specific verb (draw/generate), the resource (image), the return form (image content), and the underlying API endpoint, and it enumerates the model families involved. It clearly separates itself from chat_complete by explaining that chat models with tool "chat_complete" do not belong here.

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 states the selection rule (only models whose tool is "image_generate") and names the alternative path for chat-style image models. It also adds a practical guardrail (ask for 2K or less because 4K answers may exceed what the client accepts) and routes the agent to models_get_pricing before spending, which is a genuine when-to-use precondition.

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