WCAG MCP Server

get-criterion

Retrieve detailed WCAG 2.2 success criterion information by reference number, including complete Understanding documentation for accessibility compliance.

Instructions

Gets full details for a specific WCAG success criterion by its reference number (e.g., "1.1.1", "2.4.7", "4.1.2"), including complete Understanding documentation.

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": {
      "ref_id": "<ref_id>"
    },
    "name": "get-criterion"
  }
}

Input Schema

Name	Required	Description	Default
`ref_id`	Yes	Success criterion reference number (e.g., "1.1.1", "2.4.7")

Schema Changelog

Changes observed during successful MCP inspections.

First observedv2.0.0Feb 5, 2026

TDQS

A4/5.0

Behavior3/5

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It describes the tool's function (retrieving details) and output scope ('complete Understanding documentation'), but lacks information on error handling (e.g., what happens with invalid ref_id), performance characteristics, or authentication needs. This is adequate for a read-only tool but leaves gaps in behavioral understanding.

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 a single, well-structured sentence that front-loads the core purpose and efficiently includes key details (reference number examples and output scope). There is no redundant or unnecessary information, making it highly concise and effective for its purpose.

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 tool's low complexity (one required parameter, no output schema, no annotations), the description is largely complete. It covers the purpose, parameter context, and output scope. However, it could improve by addressing potential errors or clarifying the relationship with similar sibling tools like get-success-criteria-detail, which might overlap in functionality.

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

Parameters3/5

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

The input schema has 100% description coverage, clearly documenting the ref_id parameter. The description adds minimal value beyond the schema by reinforcing the parameter's purpose ('by its reference number') and providing examples ('e.g., "1.1.1", "2.4.7"'), but does not explain semantic nuances like format constraints or validation rules. This meets the baseline for high schema coverage.

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 specific action ('Gets full details'), target resource ('WCAG success criterion'), and scope ('by its reference number'), distinguishing it from siblings like list-success-criteria (listing) or get-criteria-by-level (filtering by level). It explicitly mentions what details are included ('complete Understanding documentation'), which further clarifies its purpose.

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?

The description provides clear context for when to use this tool: to retrieve detailed information for a specific WCAG success criterion identified by its reference number. However, it does not explicitly state when not to use it or name alternatives (e.g., list-success-criteria for a broad overview or get-success-criteria-detail which might be a similar sibling tool), which prevents a score of 5.

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