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

Annotations already indicate this is not a read-only or idempotent operation, and the description adds meaningful behavioral context: the image is returned as an inline image content block (so it can be rendered by clients and seen by the model) and, critically, 'This bills the authenticated user for the generation.' That goes beyond what annotations provide and informs the agent of real-world consequences and cost.

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?

The description is two sentences, with the core action in the first sentence and essential behavioral content in the second. It avoids repeating schema details, includes necessary financial context, and provides the inline-output type without any 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?

For a generation tool with no output schema, the description covers the key action, the return format (image content block), how it's consumed, and the billing aspect. It doesn't describe failure modes or all possible client behaviors, but this is a complete enough for selecting and invoking the tool with confidence.

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 100%, so the baseline applies and the description doesn't add meaningful parameter-level detail beyond what the schema already documents. The prompt, model, and size are all explained in the schema, and the description's mention of 'text prompt' is redundant with 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?

The description opens with a specific verb and resource: 'Generate an image from a text prompt and return it inline.' This clearly distinguishes it from audio-related siblings like generate-speech and transcribe-audio, making the tool's purpose immediately understandable.

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?

The description provides clear context on when to use the tool: it is for text-to-image generation with inline image output, and explains how the result is presented to clients and the model. It doesn't explicitly exclude alternatives, but the behavior description is sufficient to guide usage for image generation rather than speech or other MCP actions.

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