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

Annotations already cover read-only, idempotent and non-destructive semantics, and the description still adds substantial context beyond them: that screenshots and errors are historical and will be empty for a fresh import, while the contrast pass is computed live from code. This is exactly the kind of asymmetry that would otherwise mislead an agent into thinking a call failed.

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?

Three tight sentences, front-loaded with what is returned, then the use case, then the caveat that prevents misreading empty results. No filler or restatement of the title.

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, so the description carries the return-value burden and does it: output shape, data freshness, and what an empty response means. For a read-only diagnostic with three simple params, nothing an agent needs to call it correctly is missing.

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 meaning by clarifying that omitting `index` targets the active design, which reinforces the (slightly redundant) schema note. No explanation of site_id or user_goal, but neither needs 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?

States a specific verb and resource and then enumerates the three concrete outputs (screenshots, distinct browser errors, WCAG contrast advisories). An agent knows exactly what comes back without opening a schema, and the contrast-advisory framing distinguishes it from screenshot-only siblings like capture_design_screenshot.

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 an explicit use case: 'self-check an import instead of asking a human to look at it,' which tells the agent when to reach for this rather than a human review or a raw screenshot. It does not name alternative tools (e.g. validate_design, capture_design_screenshot) or state exclusions, so it stops short of full routing guidance.

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