diff --git a/org.eclipse.wildwebdeveloper.tests/plugin.xml b/org.eclipse.wildwebdeveloper.tests/plugin.xml
index 189b205f55..0c434d53bc 100644
--- a/org.eclipse.wildwebdeveloper.tests/plugin.xml
+++ b/org.eclipse.wildwebdeveloper.tests/plugin.xml
@@ -5,7 +5,7 @@
          point="org.eclipse.wildwebdeveloper.json.schema">
       <schema
             pattern="dep.yml"
-            url="https://json.schemastore.org/dependabot">
+            url="https://www.schemastore.org/dependabot">
       </schema>
       <schema
             pattern="depp.yml"
diff --git a/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/TestXML.java b/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/TestXML.java
index 5e5c3d2cfb..19b72d5c80 100644
--- a/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/TestXML.java
+++ b/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/TestXML.java
@@ -12,10 +12,7 @@
  *******************************************************************************/
 package org.eclipse.wildwebdeveloper.tests;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertNotNull;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.*;
 
 import java.io.File;
 import java.io.FileOutputStream;
@@ -24,7 +21,9 @@
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.HashMap;
 import java.util.List;
+import java.util.concurrent.Callable;
 import java.util.jar.JarEntry;
 import java.util.jar.JarOutputStream;
 import java.util.stream.Collectors;
@@ -242,8 +241,8 @@ public void testXMLCatalog() throws Exception {
         // Find system.catalog in well known location from plugin
         File systemCatalog = plugin.getStateLocation().append("system-catalog.xml").toFile();
         // Parse system-catalog to check it
-        Document systemCatalogDom = DocumentBuilderFactory.newDefaultInstance().newDocumentBuilder()
-                .parse(systemCatalog);
+        Document systemCatalogDom = runWithLocalCatalogOnlyForTestXMLCatalog(
+                () -> DocumentBuilderFactory.newDefaultInstance().newDocumentBuilder().parse(systemCatalog));
 
         // root
         Node catalogNode = systemCatalogDom.getLastChild();
@@ -276,4 +275,47 @@ public void testXMLCatalog() throws Exception {
         // Uninstall bundle once again
         catalogBundle.uninstall();
     }
+
+    /**
+     * Workaround for erratic runtime exceptions because of catalog.dtd temporarily not being available online:
+     * <pre>{@code
+     *   java.io.FileNotFoundException: http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd
+     *       at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:2010)
+     *       at ...
+     *       at java.xml/javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:206)
+     *       at org.eclipse.wildwebdeveloper.tests.TestXML.testXMLCatalog(TestXML.java:246)
+     *       at java.base/java.lang.reflect.Method.invoke(Method.java:580)
+     *       at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
+     *       at java.base/java.util.ArrayList.forEach(ArrayList.java:1596)
+     * }</pre>
+     */
+    private <T> T runWithLocalCatalogOnlyForTestXMLCatalog(Callable<T> callable) throws Exception {
+        var origSysProps = new HashMap<String, String>();
+        List.of( //
+            "javax.xml.useCatalog", //
+            "javax.xml.catalog.files", //
+            "javax.xml.catalog.prefer", //
+            "javax.xml.catalog.resolve"
+        ).forEach(k -> origSysProps.put(k, System.getProperty(k)));
+
+        var catalogRedirect = Path.of("src/org/eclipse/wildwebdeveloper/tests/catalog/oasis-catalog-redirect.xml");
+        assertTrue(Files.exists(catalogRedirect));
+        // enforce usage of local catalog.dtd file
+        System.setProperty("javax.xml.useCatalog", "true");
+        System.setProperty("javax.xml.catalog.files", catalogRedirect.toUri().toString());
+        System.setProperty("javax.xml.catalog.prefer", "system");
+        System.setProperty("javax.xml.catalog.resolve", "strict");
+        try {
+        	return callable.call();
+        } finally {
+            // restore previous behaviour
+            for (var e : origSysProps.entrySet()) {
+                if (e.getValue() == null) {
+                    System.clearProperty(e.getKey());
+                } else {
+                    System.setProperty(e.getKey(), e.getValue());
+                }
+            }
+        }
+    }
 }
diff --git a/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/TestYaml.java b/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/TestYaml.java
index c585534876..287beef03d 100644
--- a/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/TestYaml.java
+++ b/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/TestYaml.java
@@ -84,11 +84,13 @@ private void testErrorFile(String name) throws Exception {
 
     @Test
     public void testSchemaExtensionPoint() throws Exception {
+        // loads remote file https://www.schemastore.org/dependabot as configured in plugin.xml
         testErrorFile("dep.yml");
     }
 
     @Test
     public void testSchemaExtensionPointUsingPlatformURL() throws Exception {
+        // loads local file platform:/plugin/org.eclipse.wildwebdeveloper.tests/resources/dependabot.json as configured in plugin.xml
         testErrorFile("depp.yml");
     }
 }
diff --git a/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/catalog/catalog-1.0.dtd b/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/catalog/catalog-1.0.dtd
new file mode 100644
index 0000000000..dbe4b27b38
--- /dev/null
+++ b/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/catalog/catalog-1.0.dtd
@@ -0,0 +1,150 @@
+<!-- copied from http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd -->
+<!-- $Id: catalog.dtd,v 1.10 2002/10/18 23:54:58 ndw Exp $ -->
+
+<!ENTITY % pubIdChars "CDATA">
+<!ENTITY % publicIdentifier "%pubIdChars;">
+<!ENTITY % partialPublicIdentifier "%pubIdChars;">
+<!ENTITY % uriReference "CDATA">
+<!ENTITY % string "CDATA">
+<!ENTITY % systemOrPublic "(system|public)">
+
+<!ENTITY % p "">
+<!ENTITY % s "">
+<!ENTITY % nsdecl "xmlns%s;">
+
+<!ENTITY % catalog "%p;catalog">
+<!ENTITY % public "%p;public">
+<!ENTITY % system "%p;system">
+<!ENTITY % uri "%p;uri">
+<!ENTITY % rewriteSystem "%p;rewriteSystem">
+<!ENTITY % rewriteURI "%p;rewriteURI">
+<!ENTITY % delegatePublic "%p;delegatePublic">
+<!ENTITY % delegateSystem "%p;delegateSystem">
+<!ENTITY % delegateURI "%p;delegateURI">
+<!ENTITY % nextCatalog "%p;nextCatalog">
+<!ENTITY % group "%p;group">
+
+<!ENTITY % local.catalog.mix "">
+<!ENTITY % local.catalog.attribs "">
+
+<!ELEMENT %catalog; (%public;|%system;|%uri;
+                     |%rewriteSystem;|%rewriteURI;
+                     |%delegatePublic;|%delegateSystem;|%delegateURI;
+                     |%nextCatalog;|%group; %local.catalog.mix;)+>
+<!ATTLIST %catalog;
+  %nsdecl;  %uriReference;    #FIXED
+    'urn:oasis:names:tc:entity:xmlns:xml:catalog'
+  prefer    %systemOrPublic;  #IMPLIED
+  xml:base  %uriReference;    #IMPLIED
+  %local.catalog.attribs;
+>
+
+<!ENTITY % local.public.attribs "">
+
+<!ELEMENT %public; EMPTY>
+<!ATTLIST %public;
+  id    ID      #IMPLIED
+  publicId  %publicIdentifier;  #REQUIRED
+  uri   %uriReference;    #REQUIRED
+  xml:base  %uriReference;    #IMPLIED
+        %local.public.attribs;
+>
+
+<!ENTITY % local.system.attribs "">
+
+<!ELEMENT %system; EMPTY>
+<!ATTLIST %system;
+  id    ID      #IMPLIED
+  systemId  %string;    #REQUIRED
+  uri   %uriReference;    #REQUIRED
+  xml:base  %uriReference;    #IMPLIED
+        %local.system.attribs;
+>
+
+<!ENTITY % local.uri.attribs "">
+
+<!ELEMENT %uri; EMPTY>
+<!ATTLIST %uri;
+  id    ID      #IMPLIED
+  name    %string;    #REQUIRED
+  uri   %uriReference;    #REQUIRED
+  xml:base  %uriReference;    #IMPLIED
+        %local.uri.attribs;
+>
+
+<!ENTITY % local.rewriteSystem.attribs "">
+
+<!ELEMENT %rewriteSystem; EMPTY>
+<!ATTLIST %rewriteSystem;
+  id    ID      #IMPLIED
+  systemIdStartString %string;  #REQUIRED
+  rewritePrefix   %string;    #REQUIRED
+        %local.rewriteSystem.attribs;
+>
+
+<!ENTITY % local.rewriteURI.attribs "">
+
+<!ELEMENT %rewriteURI; EMPTY>
+<!ATTLIST %rewriteURI;
+  id    ID      #IMPLIED
+  uriStartString  %string;    #REQUIRED
+  rewritePrefix %string;    #REQUIRED
+        %local.rewriteURI.attribs;
+>
+
+<!ENTITY % local.delegatePublic.attribs "">
+
+<!ELEMENT %delegatePublic; EMPTY>
+<!ATTLIST %delegatePublic;
+  id    ID      #IMPLIED
+  publicIdStartString %partialPublicIdentifier; #REQUIRED
+  catalog   %uriReference;    #REQUIRED
+  xml:base  %uriReference;    #IMPLIED
+        %local.delegatePublic.attribs;
+>
+
+<!ENTITY % local.delegateSystem.attribs "">
+
+<!ELEMENT %delegateSystem; EMPTY>
+<!ATTLIST %delegateSystem;
+  id    ID      #IMPLIED
+  systemIdStartString %string;  #REQUIRED
+  catalog   %uriReference;    #REQUIRED
+  xml:base  %uriReference;    #IMPLIED
+        %local.delegateSystem.attribs;
+>
+
+<!ENTITY % local.delegateURI.attribs "">
+
+<!ELEMENT %delegateURI; EMPTY>
+<!ATTLIST %delegateURI;
+  id    ID      #IMPLIED
+  uriStartString  %string;    #REQUIRED
+  catalog   %uriReference;    #REQUIRED
+  xml:base  %uriReference;    #IMPLIED
+        %local.delegateURI.attribs;
+>
+
+<!ENTITY % local.nextCatalog.attribs "">
+
+<!ELEMENT %nextCatalog; EMPTY>
+<!ATTLIST %nextCatalog;
+  id    ID      #IMPLIED
+  catalog   %uriReference;    #REQUIRED
+  xml:base  %uriReference;    #IMPLIED
+        %local.nextCatalog.attribs;
+>
+
+<!ENTITY % local.group.mix "">
+<!ENTITY % local.group.attribs "">
+
+<!ELEMENT %group; (%public;|%system;|%uri;
+                   |%rewriteSystem;|%rewriteURI;
+                   |%delegatePublic;|%delegateSystem;|%delegateURI;
+                   |%nextCatalog; %local.group.mix;)+>
+<!ATTLIST %group;
+  id    ID      #IMPLIED
+  prefer    %systemOrPublic;  #IMPLIED
+  xml:base  %uriReference;    #IMPLIED
+        %local.group.attribs;
+>
diff --git a/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/catalog/oasis-catalog-redirect.xml b/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/catalog/oasis-catalog-redirect.xml
new file mode 100644
index 0000000000..849dc82f36
--- /dev/null
+++ b/org.eclipse.wildwebdeveloper.tests/src/org/eclipse/wildwebdeveloper/tests/catalog/oasis-catalog-redirect.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE catalog PUBLIC "-//OASIS//DTD XML Catalogs V1.0//EN" "catalog-1.0.dtd">
+<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog" prefer="system">
+   <!-- Map legacy and current systemIds to the bundled local DTD -->
+   <system systemId="http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd" uri="catalog-1.0.dtd" />
+   <system systemId="https://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd" uri="catalog-1.0.dtd" />
+   <system systemId="https://docs.oasis-open.org/entity/release/1.0/catalog-1.0.dtd" uri="catalog-1.0.dtd" />
+</catalog>