diff --git a/.gitignore b/.gitignore
index 1521c8b..3b9923c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 dist
+node_modules/
diff --git a/lib/__tests__/index-test.js b/lib/__tests__/index-test.js
index de14b21..1c98fa3 100644
--- a/lib/__tests__/index-test.js
+++ b/lib/__tests__/index-test.js
@@ -8,7 +8,7 @@ var k = () => {};
 var captureWarnings = (fn) => {
   var _warn = console.warn;
   var msgs = {};
-  console.warn = (msg) => msgs[msg] = true;
+  console.warn = (id, msg) => msgs[msg] = true;
   fn();
   console.warn = _warn;
   return msgs;
diff --git a/lib/index.js b/lib/index.js
index 1dd4a86..8ca8432 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -1,42 +1,51 @@
 var React = require('react');
 var assertions = require('./assertions');
 
-var assertAccessibility = (tagName, props, children, log) => {
+var assertAccessibility = (tagName, props, children) => {
   var key;
+  var failures = [];
 
-  var tagTests = assertions.tags[tagName];
-  if (tagTests)
-    for (key in tagTests)
-      log(tagTests[key].test(tagName, props, children), tagTests[key].msg);
+  var tagTests = assertions.tags[tagName] || [];
+  for (key in tagTests)
+    if (tagTests[key] && !tagTests[key].test(tagName, props, children))
+      failures.push(tagTests[key].msg);
 
   var propTests;
   for (var propName in props) {
     if (props[propName] === null || props[propName] === undefined) continue;
-    propTests = assertions.props[propName];
-    if (propTests)
-      for (key in propTests)
-        log(propTests[key].test(tagName, props, children), propTests[key].msg);
+    propTests = assertions.props[propName] || [];
+    for (key in propTests)
+      if (propTests[key] && !propTests[key].test(tagName, props, children))
+        failures.push(propTests[key].msg);
   }
+  return failures;
 };
 
-var error = (passed, msg) => {
-  if (!passed)
-    throw new Error(msg);
+var error = (id, msg) => {
+  throw new Error('#' + id + ": " + msg);
 };
 
-var warn = (passed, msg) => {
-  if (!passed)
-    console.warn(msg);
+var warn = (id, msg) => {
+  console.warn('#' + id, msg);
 };
 
+var nextId = 0;
 module.exports = (options) => {
   var _createElement = React.createElement;
   var log = options && options.throw ? error : warn;
   React.createElement = function (type, _props, ...children) {
+    var props = _props || {};
     if (typeof type === 'string') {
-      var props = _props || {};
-      assertAccessibility(type, props, children, log);
+      var failures = assertAccessibility(type, props, children);
+      if (failures.length) {
+        // Generate an id if one doesn't exist
+        props.id = (props.id || 'a11y-' + nextId++);
+
+        for (var i = 0; i < failures.length; i++)
+          log(props.id, failures[i]);
+      }
     }
-    return _createElement.apply(this, arguments);
+    // make sure props with the id is passed down, even if no props were passed in.
+    return _createElement.apply(this, [type, props].concat(children));
   };
 };