MQL4 ERR_WEBREQUEST_INVALID_ADDRESS
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. Capture GetLastError immediately after the failed call, correct the cause, and retry only when the condition can change.
Open the Coding Agent, then choose MQL4 from the language menu.
#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);
}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.
The error number is evidence about one failed call, not a diagnosis of the whole EA. Read the API sentinel first, then call GetLastError immediately because that function returns the current _LastError value and resets it.
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.
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.
| Check | Action |
|---|---|
| The URL is empty or lacks an http or https scheme | Reject empty URLs and require an explicit http or https scheme. |
| Whitespace, control characters, or bad string concatenation corrupts the address | Trim and validate configurable host and path values before concatenation. |
| A path or query value is inserted without proper URL construction | Encode dynamic query values according to the remote API contract. |
| The code logs only the error and hides the final URL | Log a redacted final URL and the WebRequest return value on failure. |
The script rejects a URL without an HTTP scheme and logs WebRequest failure immediately. Add the host to MT4’s allowed URL list before testing.
The example improves validation and logging. It does not prove the operation will be accepted by a broker or behave safely in live trading.
#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);
}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 AgentStatic diagnostics do not prove runtime behavior, backtest results, broker compatibility, or live-trading safety.
Check the API return value before interpreting an error number from the log.
Call GetLastError immediately and record error 5200, symbol, prices, volume, ticket, and terminal state relevant to the operation.
Reject empty URLs and require an explicit http or https scheme.
Compile the revised source, then test with the same MT4 build, broker, symbol, account permissions, and market state.
ERR_WEBREQUEST_INVALID_ADDRESS means invalid URL. The code should still identify which API returned failure and log the inputs used for that call.
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
Do not retry the same invalid address. Correct the URL construction first.
It reports the current _LastError value and resets it. Other operations can change the error state, so a delayed read may describe the wrong call.
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.
Last verified against the linked official references on . Compile and test the final source in the MetaTrader 4 build, broker, symbol, and account environment you plan to use.
Define the requirement, inspect the generated source, repair diagnostics, and test the behavior in your own MT4 environment.
Open Coding Agent