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MQL4 ERR_WEBREQUEST_REQUEST_FAILED

MQL4 error 5203 HTTP request failed: diagnose WebRequest

MQL4 error 5203 HTTP request failed maps to ERR_WEBREQUEST_REQUEST_FAILED: HTTP request failed. WebRequest failed at the request stage. Record the actual error: invalid address, connection failure, and timeout have separate codes 5200, 5201, and 5202. A received HTTP 4xx/5xx status is also different from a -1 function failure. For API calls, check the return value and capture GetLastError after a documented failure. Critical runtime errors require preventive guards and inspection of the terminal log.

Open MQL4 Coding AgentReview the code example

Open the Coding Agent, then choose MQL4 from the language menu.

WebRequestFailureDiagnostic.mq4MQL4
#property strict
#property script_show_inputs

input string Url = "https://example.com/health";

void OnStart()
  {
   if(StringFind(Url, "http://") != 0 && StringFind(Url, "https://") != 0)
     {
      Print("Invalid URL: ", Url);
      return;
     }

   char request_data[];
   char response_data[];
   string response_headers;
   ResetLastError();
   int status = WebRequest("GET", Url, "", 5000, request_data,
                           response_data, response_headers);
   if(status == -1)
      Print("WebRequest failed. error=", GetLastError(),
            ". Check the allowed URL list and connection.");
   else
      Print("HTTP status: ", status);
  }
  • Official meaning: HTTP request failed
  • Check API results or the runtime failure log
  • Capture relevant inputs and error context
  • Retry only when the condition can change

What MQL4 error 5203 means

The official MQL4 runtime table names error 5203 ERR_WEBREQUEST_REQUEST_FAILED and defines it as “HTTP request failed.” WebRequest failed at the request stage. Record the actual error: invalid address, connection failure, and timeout have separate codes 5200, 5201, and 5202. A received HTTP 4xx/5xx status is also different from a -1 function failure.

An error-state value is supporting context, not proof that a call failed or a diagnosis of the whole EA. For noncritical API failures, read the return value and then GetLastError, which resets _LastError. Critical errors such as zero division terminate execution, so code after the failing expression cannot serve as a recovery handler.

Check these conditions before editing the strategy

Start with the inputs and external state that existed at the failure point. A later log entry or a successful call can overwrite the useful context.

  • The host is missing from the terminal list of allowed URLs
  • The terminal has no connection or the request times out
  • TLS, DNS, proxy, firewall, or endpoint availability blocks the request
  • The call is attempted in Strategy Tester, where WebRequest is unavailable

Fix the cause, then choose a retry policy

Use a bounded delayed retry only for a transient network or server failure. Do not retry invalid permissions, tester restrictions, or malformed requests.

Keep the original trading and risk rules intact. A workaround that widens stops, increases volume, changes an account setting, or ignores a failed return value can hide the symptom while changing the system.

CheckAction
The host is missing from the terminal list of allowed URLsAdd the exact scheme and host to the allowed URL list when the endpoint is trusted.
The terminal has no connection or the request times outUse a bounded timeout and log connection state and elapsed time.
TLS, DNS, proxy, firewall, or endpoint availability blocks the requestTest the endpoint and certificate path outside the EA without exposing secrets.
The call is attempted in Strategy Tester, where WebRequest is unavailableProvide deterministic test data instead of calling WebRequest in Strategy Tester.

Review the complete example

The script checks a URL prefix, uses a five-second timeout, and separates -1 from an HTTP status. Its invalid-input branch prints the URL verbatim, so use non-sensitive test input and add redaction before adapting it to authenticated endpoints. No response body is validated.

The example improves validation and logging. It does not prove the operation will be accepted by a broker or behave safely in live trading.

WebRequestFailureDiagnostic.mq4MQL4
#property strict
#property script_show_inputs

input string Url = "https://example.com/health";

void OnStart()
  {
   if(StringFind(Url, "http://") != 0 && StringFind(Url, "https://") != 0)
     {
      Print("Invalid URL: ", Url);
      return;
     }

   char request_data[];
   char response_data[];
   string response_headers;
   ResetLastError();
   int status = WebRequest("GET", Url, "", 5000, request_data,
                           response_data, response_headers);
   if(status == -1)
      Print("WebRequest failed. error=", GetLastError(),
            ". Check the allowed URL list and connection.");
   else
      Print("HTTP status: ", status);
  }
Where Pineify fits

Move from the rule to editable MQL4 source

Pineify can generate or revise one self-contained .mq4 file with MQL4-specific reference context. Its independent static checker returns MetaEditor diagnostics so you can repair source issues before testing in your own MT4 environment.

Open MQL4 Coding Agent

Static diagnostics do not prove runtime behavior, backtest results, broker compatibility, or live-trading safety.

Pineify MQL4 Coding Agent with MQL4 selected and an editable MetaTrader 4 code artifact

A practical workflow

  1. 1

    Locate the failed operation

    Check the API result, or the terminal log and source location for a critical runtime failure.

  2. 2

    Capture the error once

    For a recoverable API failure, capture GetLastError immediately. For a terminated program, preserve the terminal log. Record error 5203 and the inputs relevant to the failed operation.

  3. 3

    Correct the triggering condition

    Add the exact scheme and host to the allowed URL list when the endpoint is trusted.

  4. 4

    Retest in the target environment

    Compile the revised source, then test with the same MT4 build, broker, symbol, account permissions, and market state.

Frequently asked questions

What does MQL4 error 5203 HTTP request failed mean?

ERR_WEBREQUEST_REQUEST_FAILED means HTTP request failed. Use the API result or critical runtime log, together with the relevant inputs, to identify the failed operation.

What usually causes MQL4 error 5203?

The host is missing from the terminal list of allowed URLs. The terminal has no connection or the request times out. TLS, DNS, proxy, firewall, or endpoint availability blocks the request. The call is attempted in Strategy Tester, where WebRequest is unavailable.

Should an EA retry after error 5203?

Use a bounded delayed retry only for a transient network or server failure. Do not retry invalid permissions, tester restrictions, or malformed requests.

Why should GetLastError be called immediately?

For a noncritical API failure it reports the current _LastError value and resets it. A delayed read may describe another call. It cannot recover execution after a critical error has terminated the program.

Can Pineify fix MQL4 error 5203?

Pineify can revise a self-contained .mq4 file, add validation and error logging, and return static MetaEditor diagnostics. It cannot prove broker acceptance, account permissions, market availability, or live execution.

Compile and test the final source in the MetaTrader 4 build, broker, symbol, and account environment you plan to use.

Continue with one reviewable MQL4 file

Define the requirement, inspect the generated source, repair diagnostics, and test the behavior in your own MT4 environment.

Open Coding Agent