diff --git a/js/grunt/Gruntfile.js b/js/grunt/Gruntfile.js
index ab065a330..15f60bfa2 100644
--- a/js/grunt/Gruntfile.js
+++ b/js/grunt/Gruntfile.js
@@ -453,7 +453,7 @@ module.exports = function( grunt ) {
 
       const filePath = `${buildDirectory}/${new Date().toLocaleString().split( ', ' ).join( '_' ).split( '/' ).join( '-' ).split( ' ' ).join( '_' ).split( ':' ).join( '.' )}.json`;
 
-      const api = await generatePhetioAPI( repo, buildLocal.localTestingURL );
+      const api = await generatePhetioAPI( repo, false );
       writeFile( filePath, api );
     } )
   );
diff --git a/js/grunt/phet-io/copySupplementalPhetioFiles.js b/js/grunt/phet-io/copySupplementalPhetioFiles.js
index 14d6e99c5..98e33b6ee 100644
--- a/js/grunt/phet-io/copySupplementalPhetioFiles.js
+++ b/js/grunt/phet-io/copySupplementalPhetioFiles.js
@@ -266,7 +266,7 @@ module.exports = async ( repo, version, simulationDisplayName, packageObject, bu
   await handleJSDOC( buildDir );
 
   if ( generatePhetioAPIFile ) {
-    const fullAPI = await generatePhetioAPI( repo, buildLocal.localTestingURL );
+    const fullAPI = await generatePhetioAPI( repo, true );
     grunt.file.write( `${buildDir}${repo}-phet-io-api.json`, fullAPI );
   }
 };
diff --git a/js/grunt/phet-io/generatePhetioAPI.js b/js/grunt/phet-io/generatePhetioAPI.js
index ced59c9ae..d50889bac 100644
--- a/js/grunt/phet-io/generatePhetioAPI.js
+++ b/js/grunt/phet-io/generatePhetioAPI.js
@@ -9,17 +9,53 @@
 
 'use strict';
 
+const http = require( 'http' );
+const fs = require( 'fs' );
 const puppeteer = require( 'puppeteer' );
 
 /**
  * @param {string} repo
- * @param {string} localTestingURL - the browser url to access the root of phet repos
+ * @param {boolean} [fromBuiltVersion] - if the built file should be used to generate the API (otherwise uses unbuilt)
  */
-module.exports = async ( repo, localTestingURL ) => {
-  localTestingURL = localTestingURL.endsWith( '/' ) ? localTestingURL : `${localTestingURL}/`;
+module.exports = async ( repo, fromBuiltVersion = false ) => {
 
-  return new Promise( async ( resolve, reject ) => {
+  // Consider using https://github.com/cloudhead/node-static or reading https://nodejs.org/en/knowledge/HTTP/servers/how-to-serve-static-files/
+  const server = http.createServer( ( req, res ) => {
+
+    // Trim query string
+    const tail = req.url.indexOf( '?' ) >= 0 ? req.url.substring( 0, req.url.indexOf( '?' ) ) : req.url;
+    const path = `${process.cwd()}/..${tail}`;
+
+    // See https://gist.github.com/aolde/8104861
+    const mimeTypes = {
+      html: 'text/html',
+      jpeg: 'image/jpeg',
+      jpg: 'image/jpeg',
+      png: 'image/png',
+      js: 'text/javascript',
+      css: 'text/css',
+      gif: 'image/gif',
+      mp3: 'audio/mpeg',
+      wav: 'audio/wav'
+    };
+    const mimeType = mimeTypes[ path.split( '.' ).pop() ] || 'text/plain';
+
+    fs.readFile( path, function( err, data ) {
+      if ( err ) {
+        res.writeHead( 404 );
+        res.end( JSON.stringify( err ) );
+      }
+      else {
+        res.writeHead( 200, { 'Content-Type': mimeType } );
+        res.end( data );
+      }
+    } );
+  } );
+  server.listen( 0 );
 
+  const port = server.address().port;
+
+  return new Promise( async ( resolve, reject ) => {
 
     const browser = await puppeteer.launch();
     const page = await browser.newPage();
@@ -44,10 +80,14 @@ module.exports = async ( repo, localTestingURL ) => {
     page.on( 'pageerror', msg => reject( msg ) );
 
     try {
-      await page.goto( `${localTestingURL}${repo}/${repo}_en.html?brand=phet-io&phetioStandalone&phetioPrintAPI` );
+      const relativePath = fromBuiltVersion ?
+                           `build/phet-io/${repo}_all_phet-io.html` :
+                           `${repo}_en.html`;
+      const url = `http://localhost:${port}/${repo}/${relativePath}?brand=phet-io&phetioStandalone&phetioPrintAPI`;
+      await page.goto( url );
     }
     catch( e ) {
       reject( e );
     }
   } );
-};
+};
\ No newline at end of file