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MQL4 ERR_WEBREQUEST_INVALID_ADDRESS

MQL4 error 5200 invalid URL: validate WebRequest input

MQL4 error 5200 invalid URL maps to ERR_WEBREQUEST_INVALID_ADDRESS: invalid URL. WebRequest received an address that is malformed or otherwise invalid for the request. 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.

WebRequestUrlDiagnostic.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: invalid URL
  • Check API results or the runtime failure log
  • Capture relevant inputs and error context
  • Retry only when the condition can change

What MQL4 error 5200 means

The official MQL4 runtime table names error 5200 ERR_WEBREQUEST_INVALID_ADDRESS and defines it as “invalid URL.” WebRequest received an address that is malformed or otherwise invalid for the request.

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 URL is empty or lacks an http or https scheme
  • Whitespace, control characters, or bad string concatenation corrupts the address
  • A path or query value is inserted without proper URL construction
  • The code logs only the error and hides the final URL

Fix the cause, then choose a retry policy

Do not retry the same invalid address. Correct the URL construction first.

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 URL is empty or lacks an http or https schemeReject empty URLs and require an explicit http or https scheme.
Whitespace, control characters, or bad string concatenation corrupts the addressTrim and validate configurable host and path values before concatenation.
A path or query value is inserted without proper URL constructionEncode dynamic query values according to the remote API contract.
The code logs only the error and hides the final URLLog a redacted final URL and the WebRequest return value on failure.

Review the complete example

The script checks only the http/https prefix, not the complete URL syntax. It prints invalid input verbatim, so use a non-sensitive test URL and add redaction before handling credentials or tokens. Allowlist the trusted server and test in an EA or script, outside Strategy Tester.

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

WebRequestUrlDiagnostic.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 5200 and the inputs relevant to the failed operation.

  3. 3

    Correct the triggering condition

    Reject empty URLs and require an explicit http or https scheme.

  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 5200 invalid URL mean?

ERR_WEBREQUEST_INVALID_ADDRESS means invalid URL. Use the API result or critical runtime log, together with the relevant inputs, to identify the failed operation.

What usually causes MQL4 error 5200?

The URL is empty or lacks an http or https scheme. Whitespace, control characters, or bad string concatenation corrupts the address. A path or query value is inserted without proper URL construction. The code logs only the error and hides the final URL.

Should an EA retry after error 5200?

Do not retry the same invalid address. Correct the URL construction first.

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 5200?

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