diff --git a/README.md b/README.md
index 05a2218..bff406e 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # gcn-classic-to-json
 
-A Kafka client instrumented with Prometheus.
+Convert GCN Classic notices to JSON.
 
 ## Configuration
 
diff --git a/gcn_classic_to_json/kafka.py b/gcn_classic_to_json/kafka.py
index 0c7b7db..e04a6cb 100644
--- a/gcn_classic_to_json/kafka.py
+++ b/gcn_classic_to_json/kafka.py
@@ -5,31 +5,45 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 #
-"""Monitor Kafka consumer connectivity."""
+"""Convert GCN Classic notices to JSON."""
 import json
 import logging
+import struct
 
 import gcn_kafka
 
 from . import metrics
+from . import notices
 
 log = logging.getLogger(__name__)
 
 
-def stats_cb(data):
-    stats = json.loads(data)
-    for broker in stats["brokers"].values():
-        metrics.broker_state.labels(broker["name"]).state(broker["state"])
+def kafka_delivered_cb(err, msg):
+    successful = not err
+    metrics.delivered.labels(msg.topic(), msg.partition(), successful).inc()
 
 
 def run():
+    binary_topic_prefix = 'gcn.classic.binary.'
+    json_topic_prefix = 'gcn.classic.json.'
+    int4 = struct.Struct("!l")
+    funcs = {
+        key: value
+        for key, value in notices.__dict__.items()
+        if key.isupper()
+    }
+
     log.info("Creating consumer")
     config = gcn_kafka.config_from_env()
     consumer = gcn_kafka.Consumer(config)
 
+    log.info("Creating producer")
+    config["client.id"] = __package__
+    config["on_delivery"] = kafka_delivered_cb
+    producer = gcn_kafka.Producer(config)
+
     log.info("Subscribing")
-    topics = list(consumer.list_topics().topics.keys())
-    consumer.subscribe(topics)
+    consumer.subscribe([binary_topic_prefix + key for key in funcs])
 
     log.info("Entering consume loop")
     while True:
@@ -39,3 +53,8 @@ def run():
                 log.error("topic %s: got error %s", topic, error)
             else:
                 log.info("topic %s: got message", topic)
+                ints = int4.iter_unpack(message.value())
+                key = topic[len(binary_topic_prefix):]
+                func = funcs[key]
+                json_data = json.dumps(func(*ints))
+                producer.produce(json_topic_prefix + key, json_data)
diff --git a/gcn_classic_to_json/metrics.py b/gcn_classic_to_json/metrics.py
index 003d406..290f477 100644
--- a/gcn_classic_to_json/metrics.py
+++ b/gcn_classic_to_json/metrics.py
@@ -7,3 +7,17 @@
 #
 """Prometheus metrics."""
 import prometheus_client
+
+received = prometheus_client.Counter(
+    "received",
+    "Kafka messages received",
+    labelnames=["topic", "partition"],
+    namespace=__package__,
+)
+
+delivered = prometheus_client.Counter(
+    "delivered",
+    "Kafka messages delivered",
+    labelnames=["topic", "partition", "successful"],
+    namespace=__package__,
+)
diff --git a/gcn_classic_to_json/notices.py b/gcn_classic_to_json/notices.py
new file mode 100644
index 0000000..d1f9e6e
--- /dev/null
+++ b/gcn_classic_to_json/notices.py
@@ -0,0 +1,10 @@
+"""
+Translation from binary formats to JSON.
+
+See https://gcn.gsfc.nasa.gov/sock_pkt_def_doc.html,
+https://github.com/nasa-gcn/gcn-schema
+"""
+
+
+def SWIFT_BAT_GRB_POS_ACK(bin):
+    return dict(ra=1e4 * bin[7], dec=1e4 * bin[8])