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WCAG Accessibility Scanner

run_accessibility_scan
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Scan any URL for WCAG 2.1 accessibility violations using axe-core (and optionally Pa11y). Get structured violations grouped by severity with fix hints.

Instructions

Scan a URL for WCAG 2.1 Level A + AA accessibility violations using Playwright + axe-core, with optional Pa11y (HTMLCS) as a second engine.

Returns structured violations grouped by severity with WCAG criteria and fix hints. Requires the target URL to be running and reachable.

ENGINES: Default: ["axe"]. Pass {"engines": ["axe", "htmlcs"]} to also run Pa11y/HTMLCS. Crossover findings are deduped server-side: an axe violation also flagged by HTMLCS is marked with alsoFlaggedBy: ["htmlcs"]. Adding HTMLCS typically grows the result by ~10-20% (mostly standalone HTMLCS findings) and adds ~2-4s wall-clock per scan.

NEXT STEP: The result includes a "scanId" field. Pass it directly to generate_fix_plan: generate_fix_plan({ scanId: "" }) Do NOT pass the full scan result object - use the scanId instead.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
urlYesFull URL to scan (e.g. http://localhost:3000/checkout)
tagsNoaxe-core rule tags to include (default: wcag2a, wcag21a, wcag2aa, wcag21aa)
compactNoReturn compact format (default: true). Set to false for the full verbose format with description, helpUrl, wcag tags, failureSummary, and full wcagCriteria fields.
enginesNoEngines to run (default: ["axe"]). Add "htmlcs" to also run Pa11y/HTMLCS for crossover validation. Configurable via .navable.json "engines".
excludeNoCSS selectors to exclude from scan
includeNoCSS selectors to limit scan scope
Behavior4/5

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

Beyond the readOnlyHint and destructiveHint annotations, the description adds that the URL must be reachable, explains engine behavior with deduping, and notes performance cost (~2-4s with HTMLCS). No contradictions.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is well-structured with sections for engines and next step, concise yet informative, and front-loaded with the main purpose. No filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity (6 params, no output schema), the description covers key aspects: engines behavior, performance, and next step. It could detail output structure more, but the mention of grouped violations and scanId is sufficient.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

With 100% schema coverage, baseline is 3. The description adds meaning for engines (deduping, default), tags, and compact format details, exceeding the schema's basic descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool scans a URL for WCAG 2.1 Level A+AA violations using Playwright and axe-core with optional Pa11y. It distinguishes from siblings by mentioning the next step of using generate_fix_plan with the scanId.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It provides context for when to use the tool (scanning a URL) and directs the next step to generate_fix_plan. It does not explicitly state when not to use it or compare with alternatives, but the sibling distinction is clear.

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

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