diff --git a/diagnostic.md b/diagnostic.md
new file mode 100644
index 00000000..525c5619
--- /dev/null
+++ b/diagnostic.md
@@ -0,0 +1,52 @@
+# Diagnose YunoHost functioning
+
+If you have successfully [installed](/install) YunoHost and passed through the [post-installation](/postinstall), you probably have a **working server**.
+
+## Test it
+
+In a web browser, access to your server via the domain name you just entered at the post-installation step.
+
+For example: `http://mydomain.com`
+
+
+<div class="alert alert-warning">
+If you have taken a <b>.nohost.me</b> or a <b>.noho.st</b> domain, you may have to wait 5 min before the address is reachable.
+</div>
+
+---
+
+#### If that does not work...
+
+### <small>1.</small> Have you configured your DNS well ?
+
+<div class="alert alert-info">
+This step is not necessary if you have a <b>.nohost.me</b> or a <b>.noho.st</b> domain
+</div>
+
+Go to https://www.whatsmydns.net/ , enter your domain name in the field and click `Search`.    
+If you do not see your IP address, or if there is red crosses everywhere, then you have probably misconfigured your [DNS](/dns).
+
+---
+
+### <small>2.</small> Do network ports are opened on your router ?
+
+If your DNS is well configured, and your server looks is accessible locally, you may have **network ports blocked** or not forwarded by your router.    
+In order to verify that, try accessing your server with a client outside your local network. For example via another WiFi access point or with your mobile phone in 3G/4G.
+
+If the server is unreachable outside of your local network, then the problem probably comes from your router's configuration.
+
+<div class="alert alert-info">
+Try to activate uPnP in your router's configuration interface, and check that your server is plugged in Ethernet directly behind it.
+<p>
+You can also redirect ports manually to your server's local IP address on this router's configuration interface.
+</p>
+</div>
+
+---
+
+### <small>3.</small> Do your router has hairpinning ?
+
+If the server is accessible from outside your local network, but unreachable with its domain name on the local network, then your router probably lacks of <a href="http://en.wikipedia.org/wiki/Hairpinning" target="_blank">hairpinning</a>.
+
+You cannot avoid that in a simple way. If you know how to do it, juste configure the `/etc/hosts` of your local clients to access your server with the local IP. Else, retry the installation with a **.nohost.me** or **.noho.st** domain.
+