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

The description adds some behavioral context beyond the annotations by noting that selector controls which element is rendered. It does not mention side effects like storage, cost, or returned URL behavior, but destructiveHint and readOnlyHint already communicate that this is a mutating creation operation. The description neither contradicts nor substantially extends the annotation-provided behavioral profile.

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 no filler. The primary purpose is front-loaded, and the selector guidance is placed exactly where it is actionable. Every word earns its place.

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 tool with a very rich input schema, full schema coverage, and an output schema present, the description is sufficiently complete. It leaves no critical call-invocation gap; the main missing piece is explicit routing to create_url_image or create_template, but the schema and sibling names compensate.

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 schema carries the parameter documentation burden. The description still adds value by explaining the purpose of `selector` and reinforcing that `content` should be self-contained HTML and CSS. This is a meaningful semantic addition beyond the raw 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?

The description states a specific action and resource: 'Creates an image from self-contained HTML and CSS.' It distinguishes itself from likely siblings like create_url_image by emphasizing 'self-contained HTML and CSS', and the selector note adds further precision. This is far more specific than the generic title.

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 phrase 'self-contained HTML and CSS' clearly frames when this tool is appropriate versus URL or template-based tools. 'Use selector when you want exact control over which element is rendered' gives useful situational guidance. It does not explicitly name sibling alternatives or exclusions, but the context is clear enough.

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