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A11y Expert MCP

A11y Expert MCP

by Elizabeth1979
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
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check_contrast

Evaluate two hex colors against WCAG contrast standards. Returns ratio and pass/fail for AA and AAA levels.

Instructions

Check if two colors meet WCAG contrast ratio requirements.

Args:
    foreground: Foreground color as hex (e.g., "#333333" or "333").
    background: Background color as hex (e.g., "#ffffff" or "fff").

Returns:
    Contrast ratio and pass/fail for WCAG AA and AAA levels.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "foreground": "<foreground>",
      "background": "<background>"
    },
    "name": "check_contrast"
  }
}

Input Schema

NameRequiredDescriptionDefault
foregroundYes
backgroundYes

Output Schema

NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.2/5.0
Behavior3/5

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

Partially discloses behavior by describing return values (ratio and pass/fail), but does not cover error handling, side effects, or authentication needs. Without annotations, more detail would be beneficial.

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?

Two concise paragraphs covering purpose, arguments, and returns. No unnecessary words, well-structured for quick scanning.

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

Completeness5/5

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

Complete for a simple two-parameter tool with output schema: describes return content, no missing context. Handles the task fully.

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

Parameters5/5

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

Adds significant meaning beyond the schema: explains hex format with examples ('#333333' or '333'), distinguishes foreground and background roles. With 0% schema coverage, description fully compensates.

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?

Clearly states the tool checks if two colors meet WCAG contrast ratio requirements, specifying use of hex colors and pass/fail for AA and AAA. Distinguishes from siblings like get_pattern and list_patterns which serve different purposes.

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

Usage Guidelines3/5

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

Implies usage for accessibility contrast checking but lacks explicit guidance on when to use this tool versus alternatives, or any conditions where it should not be used. No exclusions or context provided.

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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