diff --git a/CHANGELOG.md b/CHANGELOG.md
index 81f826a4b72..a8f58603947 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -83,6 +83,7 @@ Note that this project **does not** adhere to [Semantic Versioning](https://semv
 - We fixed an issue where "Specify Bib(La)TeX" tab was not focused when Bib(La)TeX was in the clipboard [#13597](https://github.com/JabRef/jabref/issues/13597)
 - We fixed an issue whereby the 'About' dialog was not honouring the user's configured font preferences. [#13558](https://github.com/JabRef/jabref/issues/13558)
 - We fixed an issue where the Pagetotal column was sorting the values alphabetically instead of numerically. [#12533](https://github.com/JabRef/jabref/issues/12533)
+- We fixed an issue where URLs starting with "www." (without a protocol) in file fields caused an `IllegalArgumentException: URI is not absolute` error. [#12186](https://github.com/JabRef/jabref/issues/12186)
 - We fixed the dark mode of the BibTeX Source dialog in the Citation Relations tab. [#13599](https://github.com/JabRef/jabref/issues/13599)
 - We fixed an issue where the LibreOffice integration did not support citation keys containing Unicode characters. [#13301](https://github.com/JabRef/jabref/issues/13301)
 - We fixed an issue where the "Search ShortScience" action did not convert LaTeX-formatted titles to Unicode. [#13418](https://github.com/JabRef/jabref/issues/13418)
diff --git a/jablib/src/main/java/org/jabref/logic/util/URLUtil.java b/jablib/src/main/java/org/jabref/logic/util/URLUtil.java
index a77e96829f6..323c2fbd523 100644
--- a/jablib/src/main/java/org/jabref/logic/util/URLUtil.java
+++ b/jablib/src/main/java/org/jabref/logic/util/URLUtil.java
@@ -81,6 +81,15 @@ public static String cleanGoogleSearchURL(String url) {
     /// @param url the String to check for a URL
     /// @return true if `url` contains a valid URL
     public static boolean isURL(String url) {
+        if (url == null || url.trim().isEmpty()) {
+            return false;
+        }
+        
+        // Check if the URL has a protocol (http://, https://, ftp://)
+        if (!URL_PATTERN.matcher(url).matches()) {
+            return false;
+        }
+        
         try {
             create(url);
             return true;
@@ -100,8 +109,16 @@ public static URL create(String url) throws MalformedURLException {
         if (url == null || url.trim().isEmpty()) {
             throw new IllegalArgumentException("URL must not be null or empty.");
         }
+
+        String trimmedUrl = url.trim();
+
+        // Add https:// prefix to URLs starting with www. to make them absolute
+        if (trimmedUrl.startsWith("www.")) {
+            trimmedUrl = "https://" + trimmedUrl;
+        }
+
         try {
-            URI parsedUri = new URI(url.trim());
+            URI parsedUri = new URI(trimmedUrl);
             if (!parsedUri.isAbsolute()) {
                 throw new MalformedURLException("URI is not absolute: " + url);
             }
diff --git a/jablib/src/test/java/org/jabref/logic/importer/util/FileFieldParserTest.java b/jablib/src/test/java/org/jabref/logic/importer/util/FileFieldParserTest.java
index 87b70b7eb4f..c6f1f1dd48b 100644
--- a/jablib/src/test/java/org/jabref/logic/importer/util/FileFieldParserTest.java
+++ b/jablib/src/test/java/org/jabref/logic/importer/util/FileFieldParserTest.java
@@ -50,6 +50,12 @@ private static Stream<Arguments> stringsToParseTest() throws MalformedURLExcepti
                         List.of(),
                         ""
                 ),
+                
+                // URL starting with www. (without protocol)
+                Arguments.of(
+                        List.of(new LinkedFile("A test", URLUtil.create("https://www.yahoo.com/abc/cde.htm"), "URL")),
+                        "A test:www.yahoo.com/abc/cde.htm:URL"
+                ),
 
                 // correct input
                 Arguments.of(
diff --git a/jablib/src/test/java/org/jabref/logic/net/URLUtilTest.java b/jablib/src/test/java/org/jabref/logic/net/URLUtilTest.java
index 83b8a07afba..d577c179f3d 100644
--- a/jablib/src/test/java/org/jabref/logic/net/URLUtilTest.java
+++ b/jablib/src/test/java/org/jabref/logic/net/URLUtilTest.java
@@ -118,9 +118,18 @@ void emptyUrl() {
     }
 
     @Test
-    void uriMissingScheme() {
+    void urlStartingWithWww() throws MalformedURLException {
+        // URLs starting with www. should be prefixed with https://
+        URL result = URLUtil.create("www.example.com");
+        assertNotNull(result);
+        assertEquals("https://www.example.com", result.toString());
+    }
+
+    @Test
+    void uriMissingSchemeAndNotStartingWithWww() {
+        // URLs not starting with www. and without a scheme should still throw an exception
         MalformedURLException exception = assertThrows(MalformedURLException.class, () ->
-                URLUtil.create("www.example.com"));
+                URLUtil.create("example.com"));
         assertTrue(exception.getMessage().contains("not absolute"));
     }