diff --git a/js/common/ChipperStringUtils.js b/js/common/ChipperStringUtils.js
index af7349d52..e43c5452e 100644
--- a/js/common/ChipperStringUtils.js
+++ b/js/common/ChipperStringUtils.js
@@ -3,7 +3,8 @@
 /**
  * String utilities used throughout chipper.
  *
- * @Chris Malley (PixelZoom, Inc.)
+ * @author Chris Malley (PixelZoom, Inc.)
+ * @author Michael Kauzmann (PhET Interactive Simulations)
  */
 
 /* eslint-env browser, node */
@@ -64,7 +65,7 @@
       return str.replace( new RegExp( find.replace( /[-\/\\^$*+?.()|[\]{}]/g, '\\$&' ), 'g' ), replaceWith );
     },
 
-    //TODO chipper#316 determine why this behaves differently than str.replace for some cases (eg, 'MAIN_INLINE_JAVASCRIPT')
+    // TODO chipper#316 determine why this behaves differently than str.replace for some cases (eg, 'MAIN_INLINE_JAVASCRIPT')
     /**
      * Replaces the first occurrence of {string} find with {string} replaceWith in {string} str
      *
@@ -122,7 +123,7 @@
 
     /**
      * Recurse through a string file and format each string value appropriately
-     * @param {Object.<string, intermediary:Object|{value:string}>} stringObject - if "intermediary", then recurse to
+     * @param {Object.<string, intermediary:Object|{value:string}>} stringsMap - if "intermediary", then recurse to
      *                                                                             find more nested keys
      * @param {boolean} isRTL - is right to left language
      */
@@ -216,6 +217,45 @@
         // It would be really strange for there to be no fallback for a certain string, that means it exists in the translation but not the original English
         throw new Error( `no entry for string key: ${key}` );
       }
+    },
+
+    /**
+     * Call a function on each string object in a string map. Recursively dive into each object that doesn't have a
+     * `value` to find nested string objects too.
+     * @param {Object.<string, Object|{value:string}>} map - string map, like a loaded JSON strings file
+     * @param {function(key:string, {value:string})} func
+     * @public
+     */
+    forEachString( map, func ) {
+      forEachStringImplementation( '', map, func );
+    },
+
+    /**
+     * @type {string}
+     * @pubic
+     */
+    A11Y_STRING_KEY_NAME: A11Y_STRING_KEY_NAME
+  };
+
+  /**
+   * This implementation function helps keep a better api for `forEachString`.
+   * @param {string} keySoFar - as we recurse down, build up a string of the key separated with dots.
+   * @param {Object} map - string key map
+   * @param {function(key:string, {value:string})} func
+   */
+  const forEachStringImplementation = ( keySoFar, map, func ) => {
+    for ( const key in map ) {
+      if ( map.hasOwnProperty( key ) ) {
+        const nextKey = keySoFar ? `${keySoFar}.${key}` : key; // don't start with period
+        if ( map[ key ].value ) {
+          func( nextKey, map[ key ] );
+        }
+        else {
+
+          // recurse to the next level since this wasn't the `value` key
+          forEachStringImplementation( nextKey, map[ key ], func );
+        }
+      }
     }
   };
 
diff --git a/js/grunt/reportUnusedStrings.js b/js/grunt/reportUnusedStrings.js
index c4d992030..5a2a3d7ef 100644
--- a/js/grunt/reportUnusedStrings.js
+++ b/js/grunt/reportUnusedStrings.js
@@ -15,6 +15,7 @@
 'use strict';
 
 const grunt = require( 'grunt' );
+const ChipperStringUtils = require( '../common/ChipperStringUtils' );
 
 /**
  * @param {string} repo
@@ -28,7 +29,7 @@ module.exports = function( repo, requirejsNamespace ) {
   // iterate over the strings
   for ( const key in jsStrings ) {
 
-    if ( jsStrings.hasOwnProperty( key ) && key !== 'a11y' ) {
+    if ( jsStrings.hasOwnProperty( key ) ) {
 
       const string = jsStrings[ key ].value;
       const requireStringKey = requirejsNamespace + '/' + key;
@@ -36,9 +37,33 @@ module.exports = function( repo, requirejsNamespace ) {
       // global.phet.chipper.strings is initialized by the string plugin
       const chipperStrings = global.phet.chipper.strings || {};
 
-      // If this string was not added to the global chipperStrings, it was not required in the sim
-      if ( !chipperStrings.hasOwnProperty( requireStringKey ) ) {
-        grunt.log.warn( `Unused string: key=${requireStringKey}, value=${string}` );
+      /**
+       * Warn if the string is not used.
+       * @param {string} fullKey - with the `REPO/` included
+       * @param {string} key - just the key, no `REPO/`
+       * @param {string} value - the value of the string
+       */
+      const warnIfStringUnused = ( fullKey, key, value ) => {
+
+        // If this string was not added to the global chipperStrings, it was not required in the sim
+        if ( !chipperStrings.hasOwnProperty( fullKey ) ) {
+          grunt.log.warn( `Unused string: key=${key}, value=${value}` );
+        }
+      };
+
+      // for top level strings
+      warnIfStringUnused( requireStringKey, key, string );
+
+      // support nesting into a11y strings
+      if ( key === ChipperStringUtils.A11Y_STRING_KEY_NAME ) {
+
+        const a11yStrings = jsStrings[ key ];
+
+        ChipperStringUtils.forEachString( a11yStrings, ( a11ySubKey, stringObject ) => {
+          const keyWithRepo = `${requireStringKey}.${a11ySubKey}`;
+          const fullKeyNoRepo = `${ChipperStringUtils.A11Y_STRING_KEY_NAME}.${a11ySubKey}`;
+          warnIfStringUnused( keyWithRepo, fullKeyNoRepo, stringObject.value );
+        } );
       }
     }
   }