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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the lower bar applies; the description still adds real value by noting rendering happens in a 'real browser' and warning that fullPage can miss late paint. It does not describe the returned artifact (image/blob) or size limits, keeping it from a 5.

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?

Two dense sentences, front-loaded with the core capability and then the practical capture advice. No filler or repetition of schema content.

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 6-param read-only tool with no output schema, the description covers the essential intent and the two most error-prone params (fullPage vs selector, width). It omits any note on the returned artifact or the id/path pairing requirement emphasized in the schema, so it is strong but not exhaustive.

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 baseline is 3; the description goes beyond the schema by recommending selector-based section captures over fullPage and suggesting specific viewport widths (design width, 390), which is usable guidance the schema doesn't encode. It adds no format detail for id/path/height, so not a 5.

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+resource ('Screenshot the DRAFT in a real browser') and immediately distinguishes itself from the audit siblings by explaining it is 'the only way to see compiled CSS, theme, state-driven UI and responsive layout'. An agent can tell this apart from audit_accessibility/audit_seo without opening a schema.

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 concrete invocation guidance: 'Shoot sections with `selector`' and screenshot 'at the design width and at 390'. It also implies when not to use fullPage ('fullPage can miss late paint'). It stops short of naming an alternative sibling or stating prerequisites, so it is clear context rather than explicit when/when-not routing.

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