diff --git a/backend.php b/backend.php
index 5839c0d2b..d13b2d62a 100644
--- a/backend.php
+++ b/backend.php
@@ -69,18 +69,6 @@
 		authenticate_user($link, "admin", null);
 	}
 
-	/* if (!($_SESSION["uid"] && validate_session($link)) && $op != "globalUpdateFeeds"
-		&& $op != "rss" && $op != "getUnread" && $op != "publish" && $op != "getProfiles") {
-
-		if ($op == "rpc" || $op == "viewfeed" || $op == "view") {
-			print_error_xml(6); exit;
-		} else {
-			header("Location: tt-rss.php?return=" .
-				urlencode($_SERVER['REQUEST_URI']));
-		}
-		exit;
-	} */
-
 	if (!($_SESSION["uid"] && validate_session($link)) && $op != "globalUpdateFeeds" &&
 				$op != "rss" && $op != "getUnread" && $op != "getProfiles") {
 
@@ -144,7 +132,12 @@
 	require_once "modules/pref-labels.php";
 	require_once "modules/pref-users.php";
 
-	if (!sanity_check($link)) { return; }
+	$error = sanity_check($link);
+
+	if ($error['code'] != 0) {
+		print json_encode(array("error" => $error));
+		return;
+	}
 
 	switch($op) { // Select action according to $op value.
 		case "rpc":
diff --git a/errors.php b/errors.php
index cd76d10a6..12aeffe75 100644
--- a/errors.php
+++ b/errors.php
@@ -1,7 +1,7 @@
 <?php
 	require_once "functions.php";
 
-	$ERRORS[0] = __("Unknown error");
+	$ERRORS[0] = "";
 
 	$ERRORS[1] = __("This program requires XmlHttpRequest " .
 			"to function properly. Your browser doesn't seem to support it.");
@@ -25,7 +25,7 @@
 
 	$ERRORS[9] = __("Configuration check failed");
 
-	$ERRORS[10] = __("Your version of MySQL is not currently supported. Please see 
+	$ERRORS[10] = __("Your version of MySQL is not currently supported. Please see
 		official site for more information.");
 
 	$ERRORS[11] = "[This error is not returned by server]";
diff --git a/functions.js b/functions.js
index 411c82494..ba82ebe11 100644
--- a/functions.js
+++ b/functions.js
@@ -1055,36 +1055,26 @@ function backend_sanity_check_callback(transport) {
 			return;
 		}
 
-		if (!transport.responseXML) {
-			if (!store) {
-				fatalError(3, "Sanity check: Received reply is not XML",
-					transport.responseText);
-				return;
-			}
-		}
-
-		var reply = transport.responseXML.getElementsByTagName("error")[0];
+		var reply = JSON.parse(transport.responseText);
 
 		if (!reply) {
 			fatalError(3, "Sanity check: invalid RPC reply", transport.responseText);
 			return;
 		}
 
-		var error_code = reply.getAttribute("error-code");
+		var error_code = reply['error']['code'];
 
 		if (error_code && error_code != 0) {
-			return fatalError(error_code, reply.getAttribute("error-msg"));
+			return fatalError(error_code, reply['error']['message']);
 		}
 
 		console.log("sanity check ok");
 
-		var params = transport.responseXML.getElementsByTagName("init-params")[0];
+		var params = reply['init-params'];
 
 		if (params) {
 			console.log('reading init-params...');
 
-			params = JSON.parse(params.firstChild.nodeValue);
-
 			if (params) {
 				for (k in params) {
 					var v = params[k];
diff --git a/functions.php b/functions.php
index b0c768ff8..1e9e5a576 100644
--- a/functions.php
+++ b/functions.php
@@ -2227,6 +2227,8 @@
 
 	function sanity_check($link) {
 
+		global $ERRORS;
+
 		$error_code = 0;
 		$schema_version = get_schema_version($link);
 
@@ -2245,12 +2247,7 @@
 			$error_code = 12;
 		}
 
-		if ($error_code != 0) {
-			print_error_xml($error_code);
-			return false;
-		} else {
-			return true;
-		}
+		return array("code" => $error_code, "message" => $ERRORS[$error_code]);
 	}
 
 	function file_is_locked($filename) {
@@ -2851,20 +2848,6 @@
 		return $version[1];
 	}
 
-	function print_error_xml($code, $add_msg = "") {
-		global $ERRORS;
-
-		$error_msg = $ERRORS[$code];
-
-		if ($add_msg) {
-			$error_msg = "$error_msg; $add_msg";
-		}
-
-		print "<rpc-reply>";
-		print "<error error-code=\"$code\" error-msg=\"$error_msg\"/>";
-		print "</rpc-reply>";
-	}
-
 	/**
 	 * Subscribes the user to the given feed
 	 *
diff --git a/modules/backend-rpc.php b/modules/backend-rpc.php
index bb76fd168..ea1867e0c 100644
--- a/modules/backend-rpc.php
+++ b/modules/backend-rpc.php
@@ -307,23 +307,21 @@
 			return;
 		}
 
-		// XML method
 		if ($subop == "sanityCheck") {
+			header("Content-Type: text/plain");
 
 			$_SESSION["hasAudio"] = $_REQUEST["hasAudio"] === "true";
 
-			print "<rpc-reply>";
-			if (sanity_check($link)) {
-				print "<error error-code=\"0\"/>";
+			$reply = array();
 
-				print "<init-params><![CDATA[";
-				print json_encode(make_init_params($link));
-				print "]]></init-params>";
+			$reply['error'] = sanity_check($link);
 
-				print_runtime_info($link);
+			if ($reply['error']['code'] == 0) {
+				$reply['init-params'] = make_init_params($link);
+				$reply['runtime-info'] = make_runtime_info($link);
 			}
-			print "</rpc-reply>";
 
+			print json_encode($reply);
 			return;
 		}
 
diff --git a/prefs.js b/prefs.js
index 012e0432a..2d7f9dff1 100644
--- a/prefs.js
+++ b/prefs.js
@@ -1539,23 +1539,6 @@ function clearFeedAccessKeys() {
 	return false;
 }
 
-function handle_rpc_reply(transport, scheduled_call) {
-	try {
-		if (transport.responseXML) {
-
-			if (!transport_error_check(transport)) return false;
-
-		} else {
-			notify_error("Error communicating with server.");
-		}
-
-	} catch (e) {
-		exception_error("handle_rpc_reply", e, transport);
-	}
-
-	return true;
-}
-
 function resetFeedOrder() {
 	try {
 		notify_progress("Loading, please wait...");
diff --git a/tt-rss.js b/tt-rss.js
index 3d0f53044..57b62c710 100644
--- a/tt-rss.js
+++ b/tt-rss.js
@@ -1022,58 +1022,6 @@ function showFeedsWithErrors() {
 	displayDlg('feedUpdateErrors');
 }
 
-function handle_rpc_reply(transport, scheduled_call) {
-	try {
-		if (transport.responseXML) {
-
-			if (!transport_error_check(transport)) return false;
-
-			var seq = transport.responseXML.getElementsByTagName("seq")[0];
-
-			if (seq) {
-				seq = seq.firstChild.nodeValue;
-
-				if (get_seq() != seq) {
-					//console.log("[handle_rpc_reply] sequence mismatch: " + seq);
-					return true;
-				}
-			}
-
-			var message = transport.responseXML.getElementsByTagName("message")[0];
-
-			if (message) {
-				message = message.firstChild.nodeValue;
-
-				if (message == "UPDATE_COUNTERS") {
-					console.log("need to refresh counters...");
-					setInitParam("last_article_id", -1);
-					_force_scheduled_update = true;
-				}
-			}
-
-			var counters = transport.responseXML.getElementsByTagName("counters")[0];
-
-			if (counters)
-				parse_counters(JSON.parse(counters.firstChild.nodeValue), scheduled_call);
-
-			var runtime_info = transport.responseXML.getElementsByTagName("runtime-info")[0];
-
-			if (runtime_info)
-				parse_runtime_info(JSON.parse(runtime_info.firstChild.nodeValue));
-
-			hideOrShowFeeds(getInitParam("hide_read_feeds") == 1);
-
-		} else {
-			notify_error("Error communicating with server.");
-		}
-
-	} catch (e) {
-		exception_error("handle_rpc_reply", e, transport);
-	}
-
-	return true;
-}
-
 function scheduleFeedUpdate(id, is_cat) {
 	try {
 		if (!id) {