diff --git a/raclette/tools.py b/raclette/tools.py
index 5b9c1f7..d3a5b5f 100644
--- a/raclette/tools.py
+++ b/raclette/tools.py
@@ -8,30 +8,27 @@
 from progress.bar import Bar
 import reverse_geocoder as rg
 import logging
+import tempfile
+import shutil
 
-# https://en.wikipedia.org/wiki/Private_network
+# Private network regexes
 priv_lo = re.compile(r"^127\.\d{1,3}\.\d{1,3}\.\d{1,3}$")
 priv_24 = re.compile(r"^10\.\d{1,3}\.\d{1,3}\.\d{1,3}$")
 priv_20 = re.compile(r"^192\.168\.\d{1,3}.\d{1,3}$")
 priv_16 = re.compile(r"^172.(1[6-9]|2[0-9]|3[0-1]).[0-9]{1,3}.[0-9]{1,3}$")
 
-
 def isPrivateIP(ip):
-
     return priv_lo.match(ip) or priv_24.match(ip) or priv_20.match(ip) or priv_16.match(ip)
 
-
 def defaultdictlist():
     return defaultdict(list)
 
-
 def valid_date(s):
     try:
         return datetime.datetime.strptime(s+"UTC", "%Y-%m-%dT%H:%M%Z")
     except ValueError:
         return None
 
-
 def read_ipmap_data(score):
     with bz2.open("cache/geolocations_ipmap.csv.bz2", "rt") as bz_file:
         for line in bz_file:
@@ -39,87 +36,73 @@ def read_ipmap_data(score):
             try:
                 if float(words[-1]) >= score:
                     yield (words[0].rstrip("/32"), words[2], words[3], words[5])
-            except Exception as e:
-                # ignore not well-formated lines in the csv file
+            except Exception:
                 pass
 
-
-def get_probes_info(ipmap=None):
-
+def get_probes_info(ipmap=None, refresh_cache=False):
     if ipmap is None:
         ipmap = {}
-
         for ip, city, state, country in read_ipmap_data(50):
             ipmap[ip] = "CT{}, {}, {}".format(city, state, country)
 
-    today = datetime.datetime.today()
     if not os.path.exists("cache/"):
         os.mkdir("cache")
 
-    if os.path.exists("cache/probe_info.json"):
-        # Get probe information from cache
-        cache = json.load(open("cache/probe_info.json", "r"))
-#        print("Loading probe information from cache")
+    cache_file = "cache/probe_info.json"
 
+    if os.path.exists(cache_file):
+        with open(cache_file, "r") as f:
+            cache = json.load(f)
         return cache["probes"]
 
-    else:
-        # Fetch probe information from RIPE API
-        url = "https://atlas.ripe.net/api/v2/probes/"
-        bar = None
-        probes = []
-        with requests.Session() as session:
-
-            # Fetch all pages
-            while url:
-                page = session.get(url).json()
-                if bar is None:
-                    bar = Bar(
-                        "Fetching probe information from RIPE API",
-                        max=page["count"],
-                        suffix='%(percent)d%%'
-                        )
-
-                # get city and country names
-                # coordinates = [(
-                    # probe["geometry"]["coordinates"][1],
-                    # probe["geometry"]["coordinates"][0] )
-                    # for probe in page["results"]:
-                        # if probe["geometry"] is not None
-                        # if probe["geometry"]["coordinates"] is not None ]
-
-                # cities = rg.search(coordinates)
-                # geoloc = dict(zip(coordinates, cities))
-
-                for probe in page["results"]:
-                    bar.next()
-                    try:
-                        # (lon, lat) = probe["geometry"]["coordinates"]
-                        # probe["city"] = "CT{}, {}, {}".format(geoloc[(lat,lon)]["name"], geoloc[(lat,lon)]["admin2"], geoloc[(lat,lon)]["cc"])
-                        if probe['address_v4'] in ipmap:
-                            probe["city"] = ipmap[probe["address_v4"]]
-                        elif probe['address_v6'] in ipmap:
-                            probe["city"] = ipmap[probe["address_v6"]]
-
-                        probes.append(probe)
-
-                    except TypeError:
-                        logging.debug("Error with probe: {}".format(probe))
-
-                url = page['next']
-            bar.finish()
-
-        # Save probe information to cache
-        fi = open("cache/probe_info.json", "w")
-        json.dump({
-            "probes": probes,
-            "timestamp": str(datetime.datetime.now(datetime.timezone.utc))
-            }, fi, indent=4)
-        fi.close()
-
-        return probes
+    # Fetch probe information from RIPE API
+    url = "https://atlas.ripe.net/api/v2/probes/"
+    bar = None
+    probes = []
+    with requests.Session() as session:
+        while url:
+            page = session.get(url).json()
+            if bar is None:
+                bar = Bar(
+                    "Fetching probe information from RIPE API",
+                    max=page["count"],
+                    suffix='%(percent)d%%'
+                )
+
+            for probe in page["results"]:
+                bar.next()
+                try:
+                    if probe['address_v4'] in ipmap:
+                        probe["city"] = ipmap[probe["address_v4"]]
+                    elif probe['address_v6'] in ipmap:
+                        probe["city"] = ipmap[probe["address_v6"]]
+                    probes.append(probe)
+                except TypeError:
+                    logging.debug("Error with probe: {}".format(probe))
+
+            url = page['next']
+        bar.finish()
+
+    # Atomic save to cache
+    tmp_file = tempfile.NamedTemporaryFile(delete=False, mode="w", dir="cache", suffix=".json")
+    json.dump({
+        "probes": probes,
+        "timestamp": str(datetime.datetime.now(datetime.timezone.utc))
+    }, tmp_file, indent=4)
+    tmp_file.close()
+
+    # Validate JSON before replacing
+    try:
+        with open(tmp_file.name, "r") as f:
+            json.load(f)
+    except Exception:
+        os.remove(tmp_file.name)
+        raise RuntimeError("Failed to write valid JSON")
 
+    shutil.move(tmp_file.name, cache_file)
+    return probes
 
 if __name__ == "__main__":
-    # Populate cache if empty
-    get_probes_info()
+    # Populate cache
+    get_probes_info(ipmap={})
+