JSON MCP Server

Instructions

Implementation Reference

• src/index.ts:654-715 (handler)

  Handler logic for the 'filter' tool within the CallToolRequestSchema handler. Fetches JSON from URL, extracts base data using jsonPath, and applies filtering based on condition string using inline comparison logic for >, <, >=, <=, ==, != operators.

  const { url, jsonPath, condition } = FilterArgumentsSchema.parse(args);
  const jsonData = await fetchData(url);
  
  // Get base data using jsonPath
  let baseData = JSONPath.value(jsonData, jsonPath);
  if (!Array.isArray(baseData)) {
      baseData = [baseData];
  }
  
  // Apply filter condition
  const result = baseData.filter((item: Record<string, any>) => {
      try {
          // Handle common comparison operators
          if (condition.includes(' > ')) {
              const [field, value] = condition.split(' > ').map(s => s.trim());
              const fieldName = field.replace('@.', '');
              return Number(item[fieldName]) > Number(value);
          }
          if (condition.includes(' < ')) {
              const [field, value] = condition.split(' < ').map(s => s.trim());
              const fieldName = field.replace('@.', '');
              return Number(item[fieldName]) < Number(value);
          }
          if (condition.includes(' >= ')) {
              const [field, value] = condition.split(' >= ').map(s => s.trim());
              const fieldName = field.replace('@.', '');
              return Number(item[fieldName]) >= Number(value);
          }
          if (condition.includes(' <= ')) {
              const [field, value] = condition.split(' <= ').map(s => s.trim());
              const fieldName = field.replace('@.', '');
              return Number(item[fieldName]) <= Number(value);
          }
          if (condition.includes(' == ')) {
              const [field, value] = condition.split(' == ').map(s => s.trim());
              const fieldName = field.replace('@.', '');
              const compareValue = value.startsWith('"') || value.startsWith("'") 
                  ? value.slice(1, -1) 
                  : Number(value);
              return item[fieldName] == compareValue;
          }
          if (condition.includes(' != ')) {
              const [field, value] = condition.split(' != ').map(s => s.trim());
              const fieldName = field.replace('@.', '');
              const compareValue = value.startsWith('"') || value.startsWith("'") 
                  ? value.slice(1, -1) 
                  : Number(value);
              return item[fieldName] != compareValue;
          }
          
          return false;
      } catch {
          return false;
      }
  });
  
  return {
      content: [{ 
          type: "text", 
          text: JSON.stringify(result, null, 2)
      }]
  };

• src/index.ts:395-399 (schema)

  Zod validation schema for filter tool arguments: url (string URL), jsonPath (string), condition (string). Used to parse inputs in the handler.

  const FilterArgumentsSchema = z.object({
      url: z.string().url(),
      jsonPath: z.string(),
      condition: z.string(),
  });

• src/index.ts:424-444 (registration)

  Tool registration in ListToolsRequestSchema handler. Defines 'filter' tool with name, description, and inputSchema matching the Zod schema.

      name: "filter",
      description: "Filter JSON data using conditions",
      inputSchema: {
          type: "object",
          properties: {
              url: {
                  type: "string",
                  description: "URL of the JSON data source",
              },
              jsonPath: {
                  type: "string",
                  description: "Base JSONPath expression",
              },
              condition: {
                  type: "string",
                  description: "Filter condition (e.g. @.price < 10)",
              }
          },
          required: ["url", "jsonPath", "condition"],
      },
  }