diff --git a/synapse/metrics/metric.py b/synapse/metrics/metric.py
new file mode 100644
index 0000000000..f5a98763cc
--- /dev/null
+++ b/synapse/metrics/metric.py
@@ -0,0 +1,54 @@
+# -*- coding: utf-8 -*-
+# Copyright 2015 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+class CounterMetric(object):
+
+    def __init__(self, name, keys=[]):
+        self.name = name
+        self.keys = keys # OK not to clone as we never write it
+
+        self.counts = {}
+
+        # Scalar metrics are never empty
+        if not len(keys):
+            self.counts[()] = 0
+
+    def inc(self, *values):
+        if len(values) != len(self.keys):
+            raise ValueError("Expected as many values to inc() as keys (%d)" %
+                (len(self.keys))
+            )
+
+        # TODO: should assert that the tag values are all strings
+
+        if values not in self.counts:
+            self.counts[values] = 1
+        else:
+            self.counts[values] += 1
+
+    def fetch(self):
+        return dict(self.counts)
+
+    def _render_key(self, values):
+        # TODO: some kind of value escape
+        return ",".join(["%s=%s" % kv for kv in zip(self.keys, values)])
+
+    def render(self):
+        if not len(self.keys):
+            return ["%s %d" % (self.name, self.counts[()])]
+
+        return ["%s{%s} %d" % (self.name, self._render_key(k), self.counts[k])
+                for k in sorted(self.counts.keys())]
diff --git a/tests/metrics/__init__.py b/tests/metrics/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/metrics/test_metric.py b/tests/metrics/test_metric.py
new file mode 100644
index 0000000000..a4fd52a9d5
--- /dev/null
+++ b/tests/metrics/test_metric.py
@@ -0,0 +1,61 @@
+# -*- coding: utf-8 -*-
+# Copyright 2015 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from tests import unittest
+
+from synapse.metrics.metric import CounterMetric
+
+
+class CounterMetricTestCase(unittest.TestCase):
+
+    def test_scalar(self):
+        counter = CounterMetric("scalar")
+
+        self.assertEquals(counter.render(), [
+            "scalar 0",
+        ])
+
+        counter.inc()
+
+        self.assertEquals(counter.render(), [
+            "scalar 1",
+        ])
+
+        counter.inc()
+        counter.inc()
+
+        self.assertEquals(counter.render(), [
+            "scalar 3"
+        ])
+
+    def test_vector(self):
+        counter = CounterMetric("vector", keys=["method"])
+
+        # Empty counter doesn't yet know what values it has
+        self.assertEquals(counter.render(), [])
+
+        counter.inc("GET")
+
+        self.assertEquals(counter.render(), [
+            "vector{method=GET} 1",
+        ])
+
+        counter.inc("GET")
+        counter.inc("PUT")
+
+        self.assertEquals(counter.render(), [
+            "vector{method=GET} 2",
+            "vector{method=PUT} 1",
+        ])