diff --git a/core/block.js b/core/block.js
index ff5907e43..c8eda7d08 100644
--- a/core/block.js
+++ b/core/block.js
@@ -1107,7 +1107,7 @@ Blockly.Block.prototype.interpolate_ = function(message, args, lastDummyAlign) {
     }
   }
   goog.asserts.assert(indexCount == args.length,
-      'Message does not reference all %s arg(s).', args.length);
+      'block "%s": Message does not reference all %s arg(s).', this.type, args.length);
   // Add last dummy input if needed.
   if (elements.length && (typeof elements[elements.length - 1] == 'string' ||
       goog.string.startsWith(elements[elements.length - 1]['type'],
@@ -1449,3 +1449,20 @@ Blockly.Block.prototype.allInputsFilled = function(opt_shadowBlocksAreFilled) {
 
   return true;
 };
+
+/**
+ * This method returns a string describing this Block in developer terms (type
+ * name and ID; English only).
+ *
+ * Intended to on be used in console logs and errors. If you need a string that
+ * uses the user's native language (including block text, field values, and
+ * child blocks), use [toString()]{@link Blockly.Block#toString}.
+ * @return {string} The description.
+ */
+Blockly.Block.prototype.toDevString = function() {
+  var msg = this.type ? '"' + this.type + '" block' : 'Block';
+  if (this.id) {
+    msg += ' (id="' + this.id + '")';
+  }
+  return msg;
+};
diff --git a/core/blockly.js b/core/blockly.js
index a3eeb68df..558c72014 100644
--- a/core/blockly.js
+++ b/core/blockly.js
@@ -405,9 +405,15 @@ Blockly.jsonInitFactory_ = function(jsonDef) {
  */
 Blockly.defineBlocksWithJsonArray = function(jsonArray) {
   for (var i = 0, elem; elem = jsonArray[i]; i++) {
-    Blockly.Blocks[elem.type] = {
-      init: Blockly.jsonInitFactory_(elem)
-    };
+    var typename = elem.type;
+    if (typename == null || typename === '') {
+      console.warn('Block definition #' + i +
+        ' in JSON array is missing a type attribute. Skipping.');
+    } else {
+      Blockly.Blocks[typename] = {
+        init: Blockly.jsonInitFactory_(elem)
+      };
+    }
   }
 };
 
diff --git a/core/connection.js b/core/connection.js
index 88d6878e6..c68cd704c 100644
--- a/core/connection.js
+++ b/core/connection.js
@@ -330,7 +330,9 @@ Blockly.Connection.prototype.checkConnection_ = function(target) {
     case Blockly.Connection.REASON_TARGET_NULL:
       throw 'Target connection is null.';
     case Blockly.Connection.REASON_CHECKS_FAILED:
-      throw 'Connection checks failed.';
+      var msg = 'Connection checks failed. ';
+      msg += this + ' expected '  + this.check_ + ', found ' + target.check_;
+      throw msg;
     case Blockly.Connection.REASON_SHADOW_PARENT:
       throw 'Connecting non-shadow to shadow block.';
     default:
@@ -619,3 +621,33 @@ Blockly.Connection.prototype.setShadowDom = function(shadow) {
 Blockly.Connection.prototype.getShadowDom = function() {
   return this.shadowDom_;
 };
+
+/**
+ * This method returns a string describing this Connection in developer terms
+ * (English only). Intended to on be used in console logs and errors.
+ * @return {string} The description.
+ */
+Blockly.Connection.prototype.toString = function() {
+  var msg;
+  var block = this.sourceBlock_;
+  if (!block) {
+    return 'Orphan Connection';
+  } else if (block.outputConnection == this) {
+    msg = 'Output Connection of ';
+  } else if (block.previousConnection == this) {
+    msg = 'Previous Connection of ';
+  } else if (block.nextConnection == this) {
+    msg = 'Next Connection of ';
+  } else {
+    var parentInput = goog.array.find(block.inputList, function(input) {
+      return input.connection == this;
+    }, this);
+    if (parentInput) {
+      msg = 'Input "' + parentInput.name + '" connection on ';
+    } else {
+      console.warn('Connection not actually connected to sourceBlock_');
+      return 'Orphan Connection';
+    }
+  }
+  return msg + block.toDevString();
+};