diff --git a/.vscode/extensions.json b/.vscode/extensions.json
index 45ef4c9..53cc594 100644
--- a/.vscode/extensions.json
+++ b/.vscode/extensions.json
@@ -1,14 +1,17 @@
 {
     "recommendations": [
+        "editorconfig.editorconfig",
         "nhoizey.gremlins",
         "oderwat.indent-rainbow",
         "streetsidesoftware.code-spell-checker",
 
-        "ms-vscode-remote.remote-ssh-edit",
+        "ianjsikes.md-graph",
         "yzhang.markdown-all-in-one",
 
         "ms-python.python",
 
+        "ms-vscode-remote.remote-ssh-edit",
+
         "redhat.ansible",
         "redhat.vscode-yaml"
     ]
diff --git a/knowledge base/gitops.md b/knowledge base/gitops.md
index 4affe13..98aa238 100644
--- a/knowledge base/gitops.md	
+++ b/knowledge base/gitops.md	
@@ -11,14 +11,18 @@ The core idea is having a Git repository that contains **declarative** descripti
 ## Further readings
 
 - [Website]
+- [Reference]
 - [Flux]
+- [Argo CD]
 
 <!--
   References
   -->
 
 <!-- Upstream -->
-[website]: https://www.gitops.tech/
+[reference]: https://www.gitops.tech/
+[website]: https://opengitops.dev/
 
 <!-- Knowledge base -->
+[argo-cd]: kubernetes/argo-cd.md
 [flux]: kubernetes/flux.md
diff --git a/knowledge base/kubernetes/argo-cd.placeholder b/knowledge base/kubernetes/argo-cd.placeholder
new file mode 100644
index 0000000..eaaa5f7
--- /dev/null
+++ b/knowledge base/kubernetes/argo-cd.placeholder	
@@ -0,0 +1 @@
+https://argo-cd.readthedocs.io/en/stable/
diff --git a/knowledge base/kubernetes/crossplane.placeholder b/knowledge base/kubernetes/crossplane.placeholder
new file mode 100644
index 0000000..b7e1963
--- /dev/null
+++ b/knowledge base/kubernetes/crossplane.placeholder	
@@ -0,0 +1 @@
+https://www.crossplane.io/
diff --git a/knowledge base/kubernetes/k9s.placeholder b/knowledge base/kubernetes/k9s.placeholder
new file mode 100644
index 0000000..d6dfec9
--- /dev/null
+++ b/knowledge base/kubernetes/k9s.placeholder	
@@ -0,0 +1 @@
+https://k9scli.io/
diff --git a/knowledge base/kubernetes/spegel.placeholder b/knowledge base/kubernetes/spegel.placeholder
new file mode 100644
index 0000000..2d53e6f
--- /dev/null
+++ b/knowledge base/kubernetes/spegel.placeholder	
@@ -0,0 +1 @@
+https://github.com/XenitAB/spegel
diff --git a/knowledge base/kubernetes/vcluster.placeholder b/knowledge base/kubernetes/vcluster.placeholder
new file mode 100644
index 0000000..112c91a
--- /dev/null
+++ b/knowledge base/kubernetes/vcluster.placeholder	
@@ -0,0 +1,2 @@
+https://www.vcluster.com/
+https://github.com/loft-sh/vcluster