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

Annotations only cover readOnly/openWorld; the description adds genuinely non-structured context: the return format ("Returns JPEG bytes") and the per-call cost with payment scheme ("$0.009 USDC per call (x402)"). It does not disclose latency, rate limits, or whether prompts are moderated, but the cost/payment disclosure is exactly the kind of thing an agent needs and can't get from the schema.

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, zero waste, and correctly front-loaded: what it does, what it returns, what it's for, what it costs. Nothing is repeated from the schema or annotations.

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?

Complete on the essentials for a 2-parameter generation tool: purpose, output format, use cases, and cost are all covered without an output schema. It stops short on output dimensions/aspect-ratio behavior and on distinguishing itself from sibling generators, which an agent realistically needs before choosing this tool.

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 50%: "steps" is documented in the schema ("1 to 8, default 4") while "prompt" has no schema description. The description partially compensates by stating the prompt is text and describing the output, but adds nothing about step semantics or how it affects quality/cost, which is the key tuning knob here.

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?

Names a specific verb and resource ("Generate an image from a text prompt") and even identifies the underlying model (FLUX.1 schnell), which is useful scoping. However, it offers no differentiation from the crowded sibling set it sits in (image_fast, image_pro, images_generations), so an agent cannot tell from the text alone which image generator to pick.

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?

"Good for thumbnails, social posts, mockups and illustrations" gives implied use cases, which is more than nothing. But there is no when-not guidance, no prerequisites, and no pointer to the alternative generators among the siblings, so routing remains inferred rather than stated.

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