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

Adds substantial behavior beyond the readOnly/openWorld annotations: billing model ($0.015 USDC via x402, payable in-call), the 'not charged when the page cannot be loaded' guarantee, output shape (A–F grade, impact-sorted violations, statement link), and viewpoint choice. These are exactly the operational traits annotations cannot express.

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 the core capability, then layered with scope caveats, output shape, and pricing in a logical order. It is long but nearly every sentence carries distinct information for a paid tool; the enumerated rule list is slightly dense but earns its space.

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 no output schema, the description properly describes return values (grade, impact-sorted violations with WCAG criteria, element counts, selectors, fix hints, accessibility-statement link), plus payment mechanics and limitations. An agent has everything needed to call and interpret it.

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% for both parameters, so the 3 baseline applies. The description restates the mobile viewport (390 px) which the schema already documents as 390x844, and adds only the free-sample example input; it adds marginal meaning beyond the schema.

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+method: an automated accessibility audit with axe-core covering every WCAG 2.2 A/AA auto-testable rule. It enumerates concrete checks (alt text, labels, contrast, keyboard traps, ARIA, touch targets), which clearly separates it from neighboring tools like site_audit, seo_meta, and domain_compliance.

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 clear use context through the EAA/BFSG/BaFG regulatory framing and a free-sample invocation example, plus a when-not boundary ('about a third of barriers... a screening, not a certification and not legal advice'). It stops short of naming an explicit alternative tool, so the routing guidance is contextual rather than comparative.

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