diff --git a/README.md b/README.md
index 5e58206..00ac779 100644
--- a/README.md
+++ b/README.md
@@ -1,23 +1,33 @@
 # SAC Route Portal GPX Downloader
-The [Swiss Alpine Club](https://www.sac-cas.ch/en/) has a great 
-[route portal](https://www.sac-cas.ch/en/huts-and-tours/sac-route-portal/)
-for finding interesting hiking routes.
 
-However you can not download the tracks as gpx files, as they argue that the exact
-paths are subject to change and it could be dangerous to adhere too closely to them. 
+The [Swiss Alpine Club](https://www.sac-cas.ch/en/) has a great
+[route portal](https://www.sac-cas.ch/en/huts-and-tours/sac-route-portal/) for
+finding interesting hiking routes.
 
-I do agree with that, but you can draw your own routes
-and download those, mainly taking some time to draw after the route they are 
-already showing on the map.
+However you can not download the tracks as gpx files, as they argue that the
+exact paths are subject to change and it could be dangerous to adhere too
+closely to them.
 
-With this extension you can select any track and then download it as a gpx file 
+I do agree with that, but you can draw your own routes and download those,
+mainly taking some time to draw after the route they are already showing on the
+map.
+
+With this extension you can select any track and then download it as a gpx file
 (an active subscription is needed).
 
 ## Be Cautious!
-Heed their warning and do not blindly follow the gps track! Use your brain and 
-plan your route beforehand to be aware of dangerous parts and alternatives. 
 
-Take a look at their [safety instructions](https://www.sac-cas.ch/en/training-and-safety/safety/).
+Heed their warning and do not blindly follow the gps track! Use your brain and
+plan your route beforehand to be aware of dangerous parts and alternatives.
+
+Take a look at their
+[safety instructions](https://www.sac-cas.ch/en/training-and-safety/safety/).
 
 ## Contributors
+
 - wizche
+- [Michal Bryxí](mailto:michal.bryxi@gmail.com)
+
+## Contact
+
+For issue reporting contact me at [shu+gpx@vanwa.ch](mailto:shu+gpx@vanwa.ch)
diff --git a/background.js b/background.js
index 95ccd76..e69a4e3 100644
--- a/background.js
+++ b/background.js
@@ -17,26 +17,28 @@ let gpxTrack = null;
  */
 function toWGS84(point) {
   // convert LV95 into the civilian system
-  let y_aux = (point[0] - 2600000) / 1000000;
-  let x_aux = (point[1] - 1200000) / 1000000;
+  const y_aux = (point[0] - 2600000) / 1000000;
+  const x_aux = (point[1] - 1200000) / 1000000;
 
   // calculate longitude and latitude in the unit 10000"
-  let lat = 16.9023892 +
+  let lat =
+    16.9023892 +
     3.238272 * x_aux -
     0.270978 * Math.pow(y_aux, 2) -
     0.002528 * Math.pow(x_aux, 2) -
     0.0447 * Math.pow(y_aux, 2) * x_aux -
-    0.0140 * Math.pow(x_aux, 3);
+    0.014 * Math.pow(x_aux, 3);
 
-  let lon = 2.6779094 +
+  let lon =
+    2.6779094 +
     4.728982 * y_aux +
     0.791484 * y_aux * x_aux +
     0.1306 * y_aux * Math.pow(x_aux, 2) -
     0.0436 * Math.pow(y_aux, 3);
 
   // unit 10000" to 1" and seconds to degrees (dec)
-  lat = lat * 100 / 36;
-  lon = lon * 100 / 36;
+  lat = (lat * 100) / 36;
+  lon = (lon * 100) / 36;
 
   return { lat: lat, lon: lon };
 }
@@ -48,7 +50,7 @@ function toWGS84(point) {
  * @returns Track point xml node for gpx.
  */
 function toTrackPoint(point) {
-  let wgs84Point = toWGS84(point);
+  const wgs84Point = toWGS84(point);
   return `<trkpt lat="${wgs84Point.lat}" lon="${wgs84Point.lon}"/>`;
 }
 
@@ -58,7 +60,7 @@ function toTrackPoint(point) {
  * @returns Way point xml node for gpx.
  */
 function toWayPoint(point) {
-  let wgs84Point = toWGS84(point.geom.coordinates);
+  const wgs84Point = toWGS84(point.geom.coordinates);
   return `
     <wpt lat="${wgs84Point.lat}" lon="${wgs84Point.lon}">
         <ele>${point.altitude}</ele>
@@ -73,7 +75,6 @@ function toWayPoint(point) {
  * @returns Combined route number, id and route title.
  */
 function trackTitle(geoJson) {
-  const route = geoJson.segments[0];
   const book = geoJson.book_route_number
     ? `${geoJson.book_route_number} - `
     : "";
@@ -88,18 +89,25 @@ function trackTitle(geoJson) {
  * @returns Simple gpx string.
  */
 function toGpx(geoJson) {
-  let trackSegments = geoJson.segments.map((segment) => {
-    if (segment.geom == null) return "";
-    return `<trkseg>
+  const trackSegments = geoJson.segments
+    .map((segment) => {
+      if (segment.geom == null) return "";
+      return `<trkseg>
              ${segment.geom.coordinates.map(toTrackPoint).join("")}
          </trkseg>`;
-  }).join("");
+    })
+    .join("");
 
-  let endPoint = geoJson.end_point ? toWayPoint(geoJson.end_point) : "";
-  let waypoints = geoJson.waypoints
-    ? geoJson.waypoints.map((wp) => {
-      return toWayPoint(wp.reference_poi);
-    }).join("")
+  const departurePoint = geoJson.departure_point
+    ? toWayPoint(geoJson.departure_point)
+    : "";
+  const endPoint = geoJson.end_point ? toWayPoint(geoJson.end_point) : "";
+  const waypoints = geoJson.waypoints
+    ? geoJson.waypoints
+        .map((wp) => {
+          return toWayPoint(wp.reference_poi);
+        })
+        .join("")
     : "";
 
   const routeTitle = trackTitle(geoJson);
@@ -111,7 +119,7 @@ function toGpx(geoJson) {
         xsi:schemaLocation="http://www.topografix.com/GPX/1/0 http://www.topografix.com/GPX/1/0/gpx.xsd"
         version="1.0"
         creator="SAC-Tourenportal GPX Downloader">
-      ${toWayPoint(geoJson.departure_point)}
+      ${departurePoint}
       ${toWayPoint(geoJson.destination_poi)}
       ${waypoints}
       ${endPoint}
@@ -123,7 +131,7 @@ function toGpx(geoJson) {
     `;
 
   const parser = new DOMParser();
-  let xmlDoc = parser.parseFromString(xmlString, "text/xml");
+  const xmlDoc = parser.parseFromString(xmlString, "text/xml");
 
   return new XMLSerializer().serializeToString(xmlDoc.documentElement);
 }
@@ -132,26 +140,26 @@ function toGpx(geoJson) {
  * Intercept the download of GeoJSON data and save it for the background script.
  */
 function listener(details) {
-  let filter = browser.webRequest.filterResponseData(details.requestId);
-  let decoder = new TextDecoder("utf-8");
-  let encoder = new TextEncoder();
+  const filter = browser.webRequest.filterResponseData(details.requestId);
+  const decoder = new TextDecoder("utf-8");
+  const encoder = new TextEncoder();
 
-  let data = [];
+  const data = [];
   filter.ondata = (event) => {
     data.push(event.data);
   };
 
-  filter.onstop = async (event) => {
-    let blob = new Blob(data, { type: "text/html" });
-    let buffer = await blob.arrayBuffer();
-    let str = decoder.decode(buffer);
+  filter.onstop = async (_event) => {
+    const blob = new Blob(data, { type: "text/html" });
+    const buffer = await blob.arrayBuffer();
+    const str = decoder.decode(buffer);
 
     updateActiveTab(browser.tabs);
 
     filter.write(encoder.encode(str));
     filter.close();
 
-    let geoJson = JSON.parse(str);
+    const geoJson = JSON.parse(str);
     const routeTitle = trackTitle(geoJson);
     gpxTrack = { title: routeTitle, data: toGpx(geoJson) };
   };
@@ -173,6 +181,41 @@ function checkTrack(tab) {
   return tab.url.match("https://www.sac-cas.ch/.*") && gpxTrack;
 }
 
+/**
+ * Remove characters that lead to problems in common filesystems.
+ *
+ * Windows (NTFS) seems to have the most restrictions, so it is mostly sourced from there.
+ *
+ * Reserved names on windows: https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file
+ *
+ * Code comes from https://github.com/parshap/node-sanitize-filename/blob/master/index.js
+ */
+function sanitizeFilename(input) {
+  const illegal = /[\/\?<>\\:\*\|"]/g;
+  // deno-lint-ignore no-control-regex
+  const control = /[\x00-\x1f\x80-\x9f]/g;
+  const reserved = /^\.+$/;
+  const windowsReserved = /^(con|prn|aux|nul|com[0-9]|lpt[0-9])(\..*)?$/i;
+  const windowsTrailing = /[\. ]+$/;
+  const replacement = "_";
+
+  const sanitized = input
+    .replace(illegal, replacement)
+    .replace(control, replacement)
+    .replace(reserved, replacement)
+    .replace(windowsReserved, replacement)
+    .replace(windowsTrailing, replacement);
+
+  if (sanitized.length === 0) {
+    sanitized = "unnamed";
+  }
+
+  const maxLength = 250;
+  const uint8Array = new TextEncoder().encode(sanitized);
+  const truncated = uint8Array.slice(0, maxLength);
+  return new TextDecoder().decode(truncated);
+}
+
 /**
  * If a valid tack was selected, download it as a gpx file.
  */
@@ -182,12 +225,13 @@ function handleClick(tab) {
     return;
   }
 
-  let blob = new Blob([gpxTrack.data], { type: "application/gpx+xml" });
-  let objectURL = URL.createObjectURL(blob);
+  const blob = new Blob([gpxTrack.data], { type: "application/gpx+xml" });
+  const objectURL = URL.createObjectURL(blob);
 
-  let downloading = browser.downloads.download({
+  const filename = sanitizeFilename(gpxTrack.title);
+  const downloading = browser.downloads.download({
     url: objectURL,
-    filename: `${gpxTrack.title}.gpx`,
+    filename: `${filename}.gpx`,
     saveAs: true,
     conflictAction: "uniquify",
   });
@@ -202,14 +246,14 @@ function handleClick(tab) {
 /**
  * Update the download icon and text.
  */
-function updateActiveTab(tabs) {
+function updateActiveTab(_tabs) {
   function updateTab(tabs) {
     if (tabs[0]) {
       updateIcon(tabs[0]);
     }
   }
 
-  let gettingActiveTab = browser.tabs.query({
+  const gettingActiveTab = browser.tabs.query({
     active: true,
     currentWindow: true,
   });
@@ -225,11 +269,11 @@ function updateIcon(tab) {
   browser.browserAction.setIcon({
     path: hasTrack
       ? {
-        48: "icons/map.png",
-      }
+          48: "icons/map.png",
+        }
       : {
-        48: "icons/map-disabled.png",
-      },
+          48: "icons/map-disabled.png",
+        },
     tabId: tab.id,
   });
   browser.browserAction.setTitle({
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..f1b9252
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,61 @@
+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1710146030,
+        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1719075281,
+        "narHash": "sha256-CyyxvOwFf12I91PBWz43iGT1kjsf5oi6ax7CrvaMyAo=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "a71e967ef3694799d0c418c98332f7ff4cc5f6af",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..6c8eac7
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,26 @@
+{
+  description = "little-hesinde project";
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    { nixpkgs, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+      in
+      {
+        devShells.default =
+          with pkgs;
+          mkShell {
+            buildInputs = [
+              deno
+              zip
+            ];
+          };
+      }
+    );
+}
diff --git a/manifest.json b/manifest.json
index b738a29..4f2230d 100644
--- a/manifest.json
+++ b/manifest.json
@@ -1,19 +1,15 @@
 {
-
     "manifest_version": 2,
     "name": "SAC Route Portal GPX Downloader",
-    "version": "0.7",
+    "version": "0.9",
     "developer": {
         "name": "Sebastian Hugentobler",
         "url": "https://code.vanwa.ch/sebastian/sac-route-portal-gpx-fx"
     },
-
     "description": "Download gpx tracks from the sac route portal.",
-
     "icons": {
         "48": "icons/map.png"
     },
-
     "permissions": [
         "activeTab",
         "downloads",
@@ -21,13 +17,13 @@
         "webRequestBlocking",
         "https://www.sac-cas.ch/*"
     ],
-    
     "background": {
-        "scripts": ["background.js"]
+        "scripts": [
+            "background.js"
+        ]
     },
-
     "browser_action": {
         "default_icon": "icons/map.png",
         "default_title": "To GPX"
-      }
+    }
 }