How to connect external API data with MQL5 for testing purposes?

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Hi everyone,
I’m learning how MQL5 handles external web requests.
I want to understand how we can connect and fetch simple JSON data from an external API just for testing purposes (for example, weather data or demo information).

Could anyone please tell me the best method to call such data securely inside an Expert Advisor or script?
Should we use Web Requests or another approach for handling APIs in MQL5?

I really appreciate any help you can provide.
 

Please search 🔍 before you post. There are already "CodeBase" publications and "Articles" about webapi usage and JSON data handling.

Your topic has been moved to the section: Expert Advisors and Automated Trading
Please consider which section is most appropriate — https://www.mql5.com/en/forum/172166/page6#comment_49114893

 
Casey Hunt:
Hi everyone,
I’m learning how MQL5 handles external web requests.
I want to understand how we can connect and fetch simple JSON data from an external API just for testing purposes (for example, weather data or demo information).

Could anyone please tell me the best method to call such data securely inside an Expert Advisor or script?
Should we use Web Requests or another approach for handling APIs in MQL5?

I really appreciate any help you can provide. 
//+------------------------------------------------------------------+
//|                                          SimpleAPIRequest.mq5    |
//|                                      By PEDRO GOMES    |
//+------------------------------------------------------------------+
#property copyright "Learning Example"
#property version   "1.00"
#property script_show_inputs

input string API_URL = "put here you API URL";

//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
{
   //--- Variables for WebRequest
   string url = API_URL;
   string headers = "";
   string result_headers;
   char post_data[];
   char result[];
   int timeout = 5000; // 5 seconds timeout
   
   //--- Reset last error
   ResetLastError();
   
   //--- Make the HTTP GET request
   Print("Sending request to: ", url);
   int res = WebRequest(
      "GET",              // HTTP method
      url,                // URL
      headers,            // Request headers (empty for simple GET)
      timeout,            // Timeout in milliseconds
      post_data,          // POST data (empty for GET)
      result,             // Response data
      result_headers      // Response headers
   );
   
   //--- Check result
   if(res == -1)
   {
      int error_code = GetLastError();
      Print("WebRequest Error: ", error_code);
      
      if(error_code == 4060)
         Print("ERROR: URL not allowed. Add '", url, "' to allowed URLs in Tools->Options->Expert Advisors");
      else if(error_code == 5203)
         Print("ERROR: Cannot resolve URL");
      else
         Print("Check your internet connection and URL");
      
      return;
   }
   
   //--- Success! Process the response
   Print("HTTP Response Code: ", res);
   
   //--- Convert result to string
   string json_response = CharArrayToString(result, 0, WHOLE_ARRAY, CP_UTF8);
   Print("JSON Response: ", json_response);
   
   //--- Simple JSON parsing example (manual parsing)
   ParseWeatherData(json_response);
}

//+------------------------------------------------------------------+
//| Simple JSON parsing function (basic example)                     |
//+------------------------------------------------------------------+
void ParseWeatherData(string json)
{
   Print("--- Parsing JSON Data ---");
   
   //--- Find temperature value (simple string search)
   int temp_pos = StringFind(json, "\"temperature_2m\":");
   if(temp_pos >= 0)
   {
      int start = temp_pos + 17; // Length of "temperature_2m":
      int end = StringFind(json, ",", start);
      if(end < 0) end = StringFind(json, "}", start);
      
      string temp_str = StringSubstr(json, start, end - start);
      double temperature = StringToDouble(temp_str);
      
      Print("Current Temperature: ", temperature, "°C");
   }
   else
   {
      Print("Could not find temperature in response");
   }
   
   //--- For production code, consider using a proper JSON library
   //--- or more robust parsing methods
}

//+------------------------------------------------------------------+
//| Alternative: Request with headers (for APIs requiring auth)     |
//+------------------------------------------------------------------+
int WebRequestWithHeaders(string url, string api_key, string &response)
{
   string headers = "Content-Type: application/json\r\n";
   headers += "Authorization: Bearer " + api_key + "\r\n";
   
   string result_headers;
   char post_data[];
   char result[];
   int timeout = 5000;
   
   int res = WebRequest(
      "GET",
      url,
      headers,
      timeout,
      post_data,
      result,
      result_headers
   );
   
   if(res != -1)
      response = CharArrayToString(result, 0, WHOLE_ARRAY, CP_UTF8);
   
   return res;
}

//+------------------------------------------------------------------+
//| POST Request Example                                             |
//+------------------------------------------------------------------+
int PostRequestExample(string url, string json_data, string &response)
{
   string headers = "Content-Type: application/json\r\n";
   string result_headers;
   
   char post_data[];
   char result[];
   
   //--- Convert JSON string to char array
   StringToCharArray(json_data, post_data, 0, WHOLE_ARRAY, CP_UTF8);
   ArrayResize(post_data, ArraySize(post_data) - 1); // Remove null terminator
   
   int res = WebRequest(
      "POST",
      url,
      headers,
      5000,
      post_data,
      result,
      result_headers
   );
   
   if(res != -1)
      response = CharArrayToString(result, 0, WHOLE_ARRAY, CP_UTF8);
   
   return res;
}
//+------------------------------------------------------------------+
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