A11y MCP Server

Instructions

Implementation Reference

• src/index.ts:286-324 (handler)

  The handler function for the 'get_rules' tool. It extracts optional 'tags' from input arguments, calls axe.getRules() to fetch accessibility rules (filtered or all), maps them to a simplified structure (ruleId, description, help, helpUrl, tags), and returns formatted JSON content.

  async getRules(args: any) {
    const { tags } = args;
    
    try {
      // Get the axe rules
      let rules;
      
      if (tags && tags.length > 0) {
        // Filter rules by tags
        rules = axe.getRules(tags);
      } else {
        // Get all rules
        rules = axe.getRules();
      }
      
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify({
              rules: rules.map((rule: any) => ({
                ruleId: rule.ruleId,
                description: rule.description,
                help: rule.help,
                helpUrl: rule.helpUrl,
                tags: rule.tags
              }))
            }, null, 2),
          },
        ],
      };
    } catch (error) {
      console.error('[Error] Failed to get rules:', error);
      throw new McpError(
        ErrorCode.InternalError,
        `Failed to get rules: ${error instanceof Error ? error.message : String(error)}`
      );
    }
  }

• src/index.ts:89-97 (schema)

  The input schema definition for the 'get_rules' tool, specifying an optional 'tags' array parameter for filtering rules.

  inputSchema: {
    type: 'object',
    properties: {
      tags: {
        type: 'array',
        items: { type: 'string' },
        description: 'Filter rules by these tags (e.g., "wcag2a", "wcag2aa", "best-practice")',
      }
    },

• src/index.ts:86-99 (registration)

  Registration of the 'get_rules' tool in the ListTools response, including name, description, and input schema.

  {
    name: 'get_rules',
    description: 'Get information about available accessibility rules with optional filtering',
    inputSchema: {
      type: 'object',
      properties: {
        tags: {
          type: 'array',
          items: { type: 'string' },
          description: 'Filter rules by these tags (e.g., "wcag2a", "wcag2aa", "best-practice")',
        }
      },
    },
  },

• src/index.ts:166-167 (registration)

  Dispatch/registration in the CallToolRequestSchema handler switch statement, routing 'get_rules' calls to the getRules method.

  case 'get_rules':
    return await this.getRules(request.params.arguments);