Visual accessibility audit

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

Annotations declare openWorldHint=true and non-readOnly/non-idempotent, but the description adds material context annotations cannot convey: it requires authentication, has fair-use rate limits, and drives a headless browser. It does not explain why the tool is marked non-readOnly, leaving that annotation unqualified.

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 technical core is strong, but the text is padded with repeated onboarding/billing content — the WebAbility account requirement, MCP URL, and sign-in instructions appear twice across bracketed and closing sentences. The first sentence is entirely setup boilerplate rather than purpose, hurting front-loading.

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?

Prerequisites, capabilities, and sibling relationship are covered well, but with no output schema the description omits what the audit actually returns (report shape, issue list, severity). For an audit tool this leaves the agent guessing about the response.

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 all four parameters (url, fullPage, viewport, brandColors) are already documented in the schema. The description adds only the redundant note that it 'takes a URL' and gives no extra syntax or format guidance, so the baseline of 3 applies.

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 verb+resource ('Pixel-level accessibility audit using Claude vision') and enumerates the concrete issue classes it detects with WCAG references. It distinguishes itself from DOM scanners and from the sibling scan_page, so an agent can tell exactly what this tool does without opening the 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?

It explicitly routes the agent relative to an alternative: 'Complements scan_page — run both for full coverage,' and frames its niche as 'issues that DOM scanners miss.' Prerequisites (account required, not runnable in Lite) are also stated. It lacks any explicit when-not-to-use guidance, so it falls just short of a 5.

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