diff --git a/README.md b/README.md
index bda725f..25900bc 100644
--- a/README.md
+++ b/README.md
@@ -160,6 +160,25 @@ Default: `true`
 
 Indicates whether [Google AMP pages](https://www.ampproject.org/) should be ignored and not be added to the sitemap.
 
+### onAdd(url)
+
+Modify the URL before it's added to the sitemap. A false or undefined return value ignores the URL, and it will not be added to the sitemap. Useful for crawling locally before hosting.
+
+Type: `function`
+Default: `null`
+
+Example:
+
+```JavaScript
+// create generator
+const generator = SitemapGenerator(host, {
+  onAdd: (url) => {
+    // Replace host in sitemap.
+    return url.replace(host, 'https://example.com')
+  }
+});
+```
+
 ### lastMod
 
 Type: `boolean`  
diff --git a/src/index.js b/src/index.js
index 43ee7c2..f4ca05a 100644
--- a/src/index.js
+++ b/src/index.js
@@ -29,7 +29,8 @@ module.exports = function SitemapGenerator(uri, opts) {
     changeFreq: '',
     priorityMap: [],
     ignoreAMP: true,
-    ignore: null
+    ignore: null,
+    onAdd: null
   };
 
   if (!uri) {
@@ -95,14 +96,15 @@ module.exports = function SitemapGenerator(uri, opts) {
 
   // fetch complete event
   crawler.on('fetchcomplete', (queueItem, page) => {
-    const { url, depth } = queueItem;
+    const { depth } = queueItem;
+    const url = opts.onAdd ? opts.onAdd(queueItem.url) : queueItem.url;
 
     if (
-      (opts.ignore && opts.ignore(url)) ||
+      (!url || opts.ignore && opts.ignore(url)) ||
       /(<meta(?=[^>]+noindex).*?>)/.test(page) || // check if robots noindex is present
       (options.ignoreAMP && /<html[^>]+(amp|⚡)[^>]*>/.test(page)) // check if it's an amp page
     ) {
-      emitter.emit('ignore', url);
+      emitter.emit('ignore', queueItem.url);
     } else {
       emitter.emit('add', url);