diff --git a/README.md b/README.md
index 2dca44d..1b41ca8 100644
--- a/README.md
+++ b/README.md
@@ -8,6 +8,10 @@ Provide ways to send notifications to signal-cli through webhooks
 virtualenv -p python3 --system-site-packages venv
 source venv/bin/activate
 pip install -r requirements.txt
+
+# Configure
+cp signal_webhook/configuration.sample.py signal_webhook/configuration.py
+$EDITOR signal_webhook/configuration.py
 ```
 
 **Beware!** Sending messages to Signal requires `gi`, which cannot be installed
diff --git a/signal_webhook/.gitignore b/signal_webhook/.gitignore
new file mode 100644
index 0000000..7c0b746
--- /dev/null
+++ b/signal_webhook/.gitignore
@@ -0,0 +1 @@
+configuration.py
diff --git a/signal_webhook/app.py b/signal_webhook/app.py
index ffcf84e..b600c9a 100644
--- a/signal_webhook/app.py
+++ b/signal_webhook/app.py
@@ -1,6 +1,8 @@
 import typing as t
+from collections import defaultdict
 from flask import Flask, request
 from . import signal
+from . import configuration
 
 app = Flask(__name__)
 
@@ -13,6 +15,7 @@ def root() -> t.Tuple[str, int]:
 @app.route("/alertmanager", methods=["POST"])
 def alertmanager():
     data = request.get_json(cache=False)
+
     if "version" not in data or int(data["version"]) != 4:
         return "Bad API version", 400
     if "alerts" not in data:
@@ -23,5 +26,22 @@ def alertmanager():
         # Ignore
         return "OK", 200
 
+    severities = defaultdict(int)
+    alert_lines = []
     for alert in data["alerts"]:
-        ...
+        try:
+            severities[alert["labels"]["severity"]] += 1
+            alert_lines.append(
+                f"<{alert['labels']['alertname']}> {alert['annotations']['description']}"
+            )
+        except KeyError as exn:
+            alert_lines.append(f"(malformed alert — {exn})")
+
+    msg = f"[PROMETHEUS] {len(data['alerts'])} firing: "
+    msg += ", ".join([f"{count} {typ}" for typ, count in severities.items()])
+    msg += "\n\n"
+    msg += "\n".join(["* " + line for line in alert_lines])
+
+    signal.signal_send(configuration.RECIPIENTS[configuration.DEFAULT_RECIPIENT], msg)
+
+    return "OK", 200
diff --git a/signal_webhook/configuration.sample.py b/signal_webhook/configuration.sample.py
new file mode 100644
index 0000000..bc1920b
--- /dev/null
+++ b/signal_webhook/configuration.sample.py
@@ -0,0 +1,5 @@
+# Signal 'address book'
+RECIPIENTS = {"foo": "+42..."}  # FIXME
+
+# Recipient from the dict above to send to by default
+DEFAULT_RECIPIENT = "foo"  # FIXME