diff --git a/oxrlib/cache.py b/oxrlib/cache.py
index 03511d49d7f5de148ae2e9611226160bf291a97c..6792c3cf0649acfeccc08d83df6b157d5c3e5467 100644
--- a/oxrlib/cache.py
+++ b/oxrlib/cache.py
@@ -1,4 +1,5 @@
 import functools
+import json
 
 from . import errors
 
@@ -77,3 +78,10 @@ class CacheWriter(CacheBase):
 
     def open(self, path):
         return self.CacheFile(path, 'w')
+
+    def write_json(self, cache_file, thing):
+        json.dump(thing, cache_file, indent=2)
+
+    def save_rate(self, rate):
+        with self.historical(rate.timestamp.date(), rate.base) as cache_file:
+            self.write_json(cache_file, rate.serialize())