diff --git a/src/amplitude-client.js b/src/amplitude-client.js
index 6ac9402e..10089659 100644
--- a/src/amplitude-client.js
+++ b/src/amplitude-client.js
@@ -817,7 +817,7 @@ var _convertProxyObjectToRealObject = function _convertProxyObjectToRealObject(i
 AmplitudeClient.prototype.identify = function(identify_obj, opt_callback) {
   if (!this._apiKeySet('identify()')) {
     if (type(opt_callback) === 'function') {
-      opt_callback(0, 'No request sent');
+      opt_callback(0, 'No request sent', {reason: 'API key is not set'});
     }
     return;
   }
@@ -833,13 +833,16 @@ AmplitudeClient.prototype.identify = function(identify_obj, opt_callback) {
       return this._logEvent(
         Constants.IDENTIFY_EVENT, null, null, identify_obj.userPropertiesOperations, null, null, opt_callback
         );
+    } else {
+      if (type(opt_callback) === 'function') {
+        opt_callback(0, 'No request sent', {reason: 'No user property operations'});
+      }
     }
   } else {
     utils.log.error('Invalid identify input type. Expected Identify object but saw ' + type(identify_obj));
-  }
-
-  if (type(opt_callback) === 'function') {
-    opt_callback(0, 'No request sent');
+    if (type(opt_callback) === 'function') {
+      opt_callback(0, 'No request sent', {reason: 'Invalid identify input type'});
+    }
   }
 };
 
@@ -862,9 +865,15 @@ AmplitudeClient.prototype.setVersionName = function setVersionName(versionName)
  */
 AmplitudeClient.prototype._logEvent = function _logEvent(eventType, eventProperties, apiProperties, userProperties, groups, timestamp, callback) {
   _loadCookieData(this); // reload cookie before each log event to sync event meta-data between windows and tabs
-  if (!eventType || this.options.optOut) {
+  if (!eventType) {
+    if (type(callback) === 'function') {
+      callback(0, 'No request sent', {reason: 'Missing eventType'});
+    }
+    return;
+  }
+  if (this.options.optOut) {
     if (type(callback) === 'function') {
-      callback(0, 'No request sent');
+      callback(0, 'No request sent', {reason: 'optOut is set to true'});
     }
     return;
   }
@@ -928,7 +937,7 @@ AmplitudeClient.prototype._logEvent = function _logEvent(eventType, eventPropert
     }
 
     if (!this._sendEventsIfReady(callback) && type(callback) === 'function') {
-      callback(0, 'No request sent');
+      callback(0, 'No request sent', {reason: 'No events to send or upload queued'});
     }
 
     return eventId;
@@ -979,10 +988,21 @@ AmplitudeClient.prototype.logEvent = function logEvent(eventType, eventPropertie
  * @example amplitudeClient.logEvent('Clicked Homepage Button', {'finished_flow': false, 'clicks': 15});
  */
 AmplitudeClient.prototype.logEventWithTimestamp = function logEvent(eventType, eventProperties, timestamp, opt_callback) {
-  if (!this._apiKeySet('logEvent()') || !utils.validateInput(eventType, 'eventType', 'string') ||
-        utils.isEmptyString(eventType)) {
+  if (!this._apiKeySet('logEvent()')) {
+    if (type(opt_callback) === 'function') {
+      opt_callback(0, 'No request sent', {reason: 'API key not set'});
+    }
+    return -1;
+  }
+  if (!utils.validateInput(eventType, 'eventType', 'string')) {
+    if (type(opt_callback) === 'function') {
+      opt_callback(0, 'No request sent', {reason: 'Invalid type for eventType'});
+    }
+    return -1;
+  }
+  if (utils.isEmptyString(eventType)) {
     if (type(opt_callback) === 'function') {
-      opt_callback(0, 'No request sent');
+      opt_callback(0, 'No request sent', {reason: 'Missing eventType'});
     }
     return -1;
   }
@@ -1005,10 +1025,15 @@ AmplitudeClient.prototype.logEventWithTimestamp = function logEvent(eventType, e
  * @example amplitudeClient.logEventWithGroups('Clicked Button', null, {'orgId': 24});
  */
 AmplitudeClient.prototype.logEventWithGroups = function(eventType, eventProperties, groups, opt_callback) {
-  if (!this._apiKeySet('logEventWithGroup()') ||
-        !utils.validateInput(eventType, 'eventType', 'string')) {
+  if (!this._apiKeySet('logEventWithGroups()')) {
     if (type(opt_callback) === 'function') {
-      opt_callback(0, 'No request sent');
+      opt_callback(0, 'No request sent', {reason: 'API key not set'});
+    }
+    return -1;
+  }
+  if (!utils.validateInput(eventType, 'eventType', 'string')) {
+    if (type(opt_callback) === 'function') {
+      opt_callback(0, 'No request sent', {reason: 'Invalid type for eventType'});
     }
     return -1;
   }
@@ -1113,9 +1138,27 @@ var _removeEvents = function _removeEvents(scope, eventQueue, maxId) {
  * Note the server response code and response body are passed to the callback as input arguments.
  */
 AmplitudeClient.prototype.sendEvents = function sendEvents(callback) {
-  if (!this._apiKeySet('sendEvents()') || this._sending || this.options.optOut || this._unsentCount() === 0) {
+  if (!this._apiKeySet('sendEvents()')) {
+    if (type(callback) === 'function') {
+      callback(0, 'No request sent', {reason: 'API key not set'});
+    }
+    return;
+  }
+  if (this.options.optOut) {
+    if (type(callback) === 'function') {
+      callback(0, 'No request sent', {reason: 'optOut is set to true'});
+    }
+    return;
+  }
+  if (this._unsentCount() === 0) {
+    if (type(callback) === 'function') {
+      callback(0, 'No request sent', {reason: 'No events to send'});
+    }
+    return;
+  }
+  if (this._sending) {
     if (type(callback) === 'function') {
-      callback(0, 'No request sent');
+      callback(0, 'No request sent', {reason: 'Request already in progress'});
     }
     return;
   }