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

Annotations already declare readOnly, non-destructive and closed-world; the description adds genuinely new context that it is a deterministic table with nothing fetched or run, and enumerates the return payload (over-report, under-report, trust level, Puppeteer/DevTools snippet). Only the absence of an output schema keeps it from being fully self-contained.

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?

Front-loaded with what the tool is, then the parameter, then the return contract, then the null-argument case and the side-effect disclaimer. Dense but every sentence carries information an agent needs.

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?

With one optional parameter, no output schema and safety already covered by annotations, the description covers input forms, return contents and determinism. Only a concrete 'call this after X' trigger 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 baseline is 3, but the description adds value with concrete accepted value forms — tool names, WCAG numbers, plain descriptions — and a rich example list ('unnamed link', 'aria-hidden', 'carousel'), plus the omit-to-list-all behavior.

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 resource and purpose: a lookup table for the gap between static-tool readings and browser rendering, plus what it returns. It implicitly separates itself from static checkers like check_contrast or check_touch_targets, but never names a sibling explicitly.

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?

Clear context for use: consult it to learn when a static result over- or under-reports and how far to trust it, with the no-argument mode documented. However, it gives no explicit exclusions or routing to alternatives (e.g. 'use check_contrast for the static check first').

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