diff --git a/website/playground/Playground.js b/website/playground/Playground.js
index cd6ad94f..488af05c 100644
--- a/website/playground/Playground.js
+++ b/website/playground/Playground.js
@@ -113,16 +113,17 @@ class Playground extends React.Component {
               <div className="editors">
                 <InputPanel
                   mode="jsx"
+                  rulerColumn={options.printWidth}
                   value={content}
                   onChange={this.setContent}
                 />
-                {editorState.showAst ? (
-                  <DebugPanel value={"ast here"} />
-                ) : null}
-                {editorState.showDoc ? (
-                  <DebugPanel value={"doc here"} />
-                ) : null}
-                <OutputPanel mode="jsx" value={formatted} />
+                {editorState.showAst ? <DebugPanel value={"ast here"} /> : null}
+                {editorState.showDoc ? <DebugPanel value={"doc here"} /> : null}
+                <OutputPanel
+                  mode="jsx"
+                  value={formatted}
+                  rulerColumn={options.printWidth}
+                />
               </div>
             </div>
             <div className="bottom-bar">
diff --git a/website/playground/panels.js b/website/playground/panels.js
index bc058860..f7a95155 100644
--- a/website/playground/panels.js
+++ b/website/playground/panels.js
@@ -10,9 +10,10 @@ class CodeMirrorPanel extends React.Component {
   }
 
   componentDidMount() {
+    const { mode, rulerColumn: column, rulerColor: color } = this.props;
     this._codeMirror = CodeMirror.fromTextArea(
       this._textareaRef.current,
-      this.props.options
+      Object.assign({ mode, rulers: [{ column, color }] }, this.props.options)
     );
     this._codeMirror.on("change", this.handleChange);
     this._codeMirror.setValue(this.props.value || "");
@@ -22,10 +23,17 @@ class CodeMirrorPanel extends React.Component {
     this._codeMirror && this._codeMirror.toTextArea();
   }
 
-  componentDidUpdate() {
+  componentDidUpdate(prevProps) {
     if (this.props.value !== this._codeMirror.getValue()) {
       this._codeMirror.setValue(this.props.value);
     }
+    if (this.props.mode !== prevProps.mode) {
+      this._codeMirror.setOption("mode", this.props.mode);
+    }
+    if (this.props.rulerColumn !== prevProps.rulerColumn) {
+      const { rulerColumn: column, rulerColor: color } = this.props;
+      this._codeMirror.setOption("rulers", [{ column, color }]);
+    }
   }
 
   handleChange(doc, change) {
@@ -43,7 +51,7 @@ class CodeMirrorPanel extends React.Component {
   }
 }
 
-export function InputPanel({ mode, value, onChange }) {
+export function InputPanel({ mode, rulerColumn, value, onChange }) {
   return (
     <CodeMirrorPanel
       options={{
@@ -52,23 +60,27 @@ export function InputPanel({ mode, value, onChange }) {
         autoCloseBrackets: true,
         matchBrackets: true,
         showCursorWhenSelecting: true,
-        tabWidth: 2,
-        mode
+        tabWidth: 2
       }}
+      mode={mode}
+      rulerColumn={rulerColumn}
+      rulerColor="#eeeeee"
       value={value}
       onChange={onChange}
     />
   );
 }
 
-export function OutputPanel({ mode, value }) {
+export function OutputPanel({ mode, rulerColumn, value }) {
   return (
     <CodeMirrorPanel
       options={{
         readOnly: true,
-        lineNumbers: true,
-        mode
+        lineNumbers: true
       }}
+      mode={mode}
+      rulerColumn={rulerColumn}
+      rulerColor="#444444"
       value={value}
     />
   );