Index: kernel-impl/src/main/java/org/sakaiproject/util/impl/FormattedTextImpl.java
===================================================================
--- kernel-impl/src/main/java/org/sakaiproject/util/impl/FormattedTextImpl.java	(revision 127810)
+++ kernel-impl/src/main/java/org/sakaiproject/util/impl/FormattedTextImpl.java	(working copy)
@@ -34,6 +34,7 @@
 import org.apache.commons.lang.StringUtils;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.apache.commons.validator.UrlValidator;
 import org.w3c.dom.Element;
 
 import org.owasp.validator.html.AntiSamy;
@@ -1330,6 +1331,32 @@
         }
     }
 
+    /* (non-Javadoc)
+     * @see org.sakaiproject.util.api.FormattedText#validateURL(java.lang.String)
+     */
+    public boolean validateURL(String urlToValidate) {
+        if (StringUtils.isBlank(urlToValidate)) return false;
+
+        // For a protocol-relative URL, we validate with protocol attached 
+        // RFC 1808 Section 4
+        if ((urlToValidate.startsWith("//")) && (urlToValidate.indexOf("://") == -1))
+        {
+            urlToValidate = "http:" + urlToValidate;
+        }
+
+        // For a site-relative URL, we validate with host name and protocol attached 
+        // SAK-13787 SAK-23752
+        if ((urlToValidate.startsWith("/")) && (urlToValidate.indexOf("://") == -1))
+        {
+            urlToValidate = "http://127.0.0.1:8080" + urlToValidate;
+        }
+
+        // Validate the url
+        UrlValidator urlValidator = new UrlValidator();
+        return urlValidator.isValid(urlToValidate);
+    }
+
+
     // PRIVATE STUFF
 
     /**
Index: kernel-impl/pom.xml
===================================================================
--- kernel-impl/pom.xml	(revision 127810)
+++ kernel-impl/pom.xml	(working copy)
@@ -118,6 +118,11 @@
 		<artifactId>commons-lang</artifactId>
 	</dependency>
     <dependency>
+      <groupId>commons-validator</groupId>
+      <artifactId>commons-validator</artifactId>
+      <version>1.3.1</version>
+    </dependency>
+    <dependency>
         <!-- for parsing CSV data from config service files -->
         <groupId>net.sf.opencsv</groupId>
         <artifactId>opencsv</artifactId>
Index: api/src/main/java/org/sakaiproject/util/api/MockFormattedText.java
===================================================================
--- api/src/main/java/org/sakaiproject/util/api/MockFormattedText.java	(revision 127810)
+++ api/src/main/java/org/sakaiproject/util/api/MockFormattedText.java	(working copy)
@@ -172,4 +172,9 @@
         return value;
     }
 
+    public boolean validateURL(String urlToValidate) {
+        log.warn(WARNING);
+        return false;
+    }
+
 }
Index: api/src/main/java/org/sakaiproject/util/api/FormattedText.java
===================================================================
--- api/src/main/java/org/sakaiproject/util/api/FormattedText.java	(revision 127810)
+++ api/src/main/java/org/sakaiproject/util/api/FormattedText.java	(working copy)
@@ -296,7 +296,7 @@
      * previous form.
      * 
      * @param value
-     * @return
+     * @return converted text
      */
     public String convertOldFormattedText(String value);
 
@@ -356,4 +356,15 @@
      */
     public String escapeUrl(String value);
 
+    /**
+     * General utility to validate a URL.
+     * The idea is to encode the rules we have for URLs we are willing
+     * to put in src="URL" or href="URL" places within our code,
+     * relative URLs must start with "/"
+     * 
+     * @param urlToValidate a URL that might be placed in Sakai content
+     * @return true if the URL is valid OR false if it fails the tests
+     */
+    public boolean validateURL(String urlToValidate);
+
 }
\ No newline at end of file
Index: kernel-util/src/main/java/org/sakaiproject/util/FormattedText.java
===================================================================
--- kernel-util/src/main/java/org/sakaiproject/util/FormattedText.java	(revision 127810)
+++ kernel-util/src/main/java/org/sakaiproject/util/FormattedText.java	(working copy)
@@ -161,4 +161,11 @@
         return getFormattedText().decodeNumericCharacterReferences(value);
     }
 
+    /**
+     * @see org.sakaiproject.util.api.FormattedText#validateURL(String)
+     */
+    public static boolean validateURL(String urlToValidate) {
+        return getFormattedText().validateURL(urlToValidate);
+    }
+
 }
\ No newline at end of file