diff --git a/ntfy/README.org b/ntfy/README.org
new file mode 100644
index 0000000..94dcaf2
--- /dev/null
+++ b/ntfy/README.org
@@ -0,0 +1,58 @@
+# -*- ispell-local-dictionary: "english" -*-
+
+* Usage
+
+** Basic usage
+
+#+begin_src yaml
+ntfy:
+  options:
+    ## These are default of the charm (different from default of `ntfy`)
+    #auth-default-access: deny-all
+    #enable-signup: false
+    #enable-login: true
+    #enable-reservations: true
+#+end_src
+
+Any option from the help of [[https://docs.ntfy.sh/config/][ntfy]] can be used, to the exception of ~firebase-key-file~.
+
+To setup ~firebase~, there are some slight differences you can find here.
+
+
+** Connection with =Firebase=
+
+I you build your own Android/IOS ntfy app, you can use Firebase Cloud
+Messaging (FCM) to send notification through official channel. To
+configure your server to send notification with Firebase you can:
+
+#+begin_src yaml
+ntfy:
+  options:
+    firebase: ## content of your firebase service key file in yaml
+      type: service_account
+      project_id: myfirebase-project
+      private_key_id: 0ebce...41480
+      private_key: |
+        -----BEGIN PRIVATE KEY-----
+        MzynkLGbScqN4XAWCU84Q6LLi6MFsnDyrA883Cdkttg1zI62q/BohgIck+897oyb
+        ..
+        ifQT/X7DVZl42p0M1mwwdAS8Ig==
+        -----END PRIVATE KEY-----
+      client_email: firebase-adminsdk-fodhh@ntfy-0k.iam.gserviceaccount.com
+      client_id: "101777552980915316312"
+      auth_uri: https://accounts.google.com/o/oauth2/auth
+      token_uri: https://oauth2.googleapis.com/token
+      auth_provider_x509_cert_url: https://www.googleapis.com/oauth2/v1/certs
+      client_x509_cert_url: https://www.googleapis.com/robot/v1/metadata/x509/firebase-adminsdk-fxdhj%40myfirebase-project.iam.gserviceaccount.com
+#+end_src
+
+To produce the output from the private service key file you created in
+=Firebase= you could:
+
+#+begin_src sh
+cat myfirebase-project-firebase-adminsdk-fxdhj-6eaewk4a4.json | yq -p json -o yaml
+#+end_src
+
+To get more information about how to deploy your own app [[https://docs.ntfy.sh/config/#firebase-fcm][ntfy's doc
+about FCM]] might be helpful.
+
diff --git a/ntfy/lib/common b/ntfy/lib/common
index 497212a..3b54886 100644
--- a/ntfy/lib/common
+++ b/ntfy/lib/common
@@ -1,11 +1,44 @@
 # -*- mode: shell-script -*-
 
 NTFY_CONFIGFILE="$SERVICE_CONFIGSTORE/etc/ntfy/server.yml"
+NTFY_FIREBASE_KEYFILE="$SERVICE_CONFIGSTORE/etc/ntfy/firebase-key.json"
 
 ntfy:init() {
     service_def=$(get_compose_service_def "$SERVICE_NAME")
-    mkdir -p "${NTFY_CONFIGFILE%/*}" &&
-        e "$service_def" | yq e '.options' - > "$NTFY_CONFIGFILE"
+    options=$(e "$service_def" | yq e '.options' -)
+
+    mkdir -p "${NTFY_CONFIGFILE%/*}" || {
+        err "failed to create directory ${NTFY_CONFIGFILE%/*}"
+        exit 1
+    }
+
+    ## Ensure 'firebase-key-file' was not set in '$options'
+    if yq e -e '.firebase-key-file' <<< "$options" >/dev/null; then
+        err "${WHITE}firebase-key-file${NORMAL} should not be" \
+            "specified in ${DARKYELLOW}$SERVICE_NAME${NORMAL}'s options"
+        exit 1
+    fi
+
+    ## if 'firebase' is set
+    if firebase_key=$(yq e -e '.firebase' 2>/dev/null <<< "$options"); then
+        ## set 'firebase-key-file' in '$options'
+        options=$(yq e '.firebase-key-file = "/etc/ntfy/firebase-key.json"' <<< "$options") || {
+            err "failed to set firebase-key-file in options"
+            exit 1
+        }
+        umask 077
+        ## store content of $firebase_key in json format in '$NTFY_FIREBASE_KEYFILE'
+        e "$firebase_key" | yq -p yaml -o json . > "$NTFY_FIREBASE_KEYFILE" || {
+            err "failed to store firebase-key-file"
+            exit 1
+        }
+    fi
+
+    e "$options" > "$NTFY_CONFIGFILE" || {
+        err "failed to store ntfy config"
+        exit 1
+    }
+
 }
 
 ntfy:config() {