diff --git a/README.md b/README.md
index 680998d..11ad260 100644
--- a/README.md
+++ b/README.md
@@ -68,8 +68,12 @@ The bundled nginx config (`default.conf`) is more than a file server:
 - `Cache-Control: no-store` for HTML and JS, so a changed `CONFIG` takes effect
   on reload.
 
-A plain static server without these proxies (e.g. `python3 -m http.server
-58881`) runs the UI, but terrain, basemap and road data will not load.
+The proxies are a convenience, not a requirement: every data source is also
+reachable directly from the browser (ESRI, the AWS elevation bucket and the
+Overpass mirrors all answer cross-origin requests), and the page probes for
+`/terrarium/` and `/esri/...` at start-up and switches to the proxy only when
+this same-origin proxy actually exists. Running the files from any static
+server therefore works as well - just without the nginx-side Overpass cache.
 
 ## Single-file build
 
@@ -86,10 +90,14 @@ python3 build.py --check            # build to a temp file and verify, write not
 `--check` fails if anything is left that would need a sibling file (an external
 `<script src>` or a CSS `<link>`).
 
-Runtime *data* is still fetched at load (tiles, Overpass, weather): serve the
-file from the Docker image for the full experience. Opened via `file://` or a
-proxy-less server it renders sky, clouds and UI with an "OFFLINE"-labelled
-ground grid instead of basemap tiles.
+Runtime *data* is fetched at load, but from public sources only: ESRI basemap
+tiles, the AWS elevation tiles and the Overpass mirrors are all CORS-enabled,
+and Open-Meteo needs no key. So the built file runs on its own - from any
+static server, and even opened directly via `file://`. Serving it from the
+Docker image additionally gives the nginx proxies and the 30-day Overpass
+cache, which is the gentlest option for the upstreams. If a source is
+unreachable, the scene degrades instead of failing: an "OFFLINE"-labelled
+ground grid in place of basemap tiles.
 
 ## Configuration
 
diff --git a/build.py b/build.py
index 08970dd..097864d 100644
--- a/build.py
+++ b/build.py
@@ -15,12 +15,11 @@ What gets inlined:
                                               (window.__inlineThemeCss, so
                                                theme switching works offline)
 
-The result needs no sibling files. Runtime DATA is still fetched on load:
-basemap and elevation tiles, Overpass road/settlement cells and the Open-Meteo
-weather API. Serve the file from the same nginx as the development site (its
-CORS proxies make the tiles reachable) or open it with a warm IndexedDB cache
-for fully offline rendering. Opened via file:// it still runs sky, clouds,
-terrain shading and the whole UI, just without the textured ground.
+The result needs no sibling files and no server of ours: basemap tiles, the
+elevation tiles and the Overpass mirrors are all CORS-enabled public sources,
+so the file runs from any static host or straight from disk (file://). The
+bundled nginx is optional - it adds the same-origin proxies and a 30-day
+Overpass cache, which is the gentlest way to hit those upstreams.
 
 The build fails loudly if any external script or stylesheet reference survives.
 """
diff --git a/vendor/clouds3d.js b/vendor/clouds3d.js
index 1173b7f..0edebcc 100644
--- a/vendor/clouds3d.js
+++ b/vendor/clouds3d.js
@@ -826,12 +826,20 @@ function init(canvas) {
 // Tile source per CONFIG.ground.style:
 //   'streets'    - ESRI World_Street_Map (place names), /esri/streets/
 //   'satellite'  - ESRI World_Imagery (no labels), /esri/imagery/
-// Both are z11 {z}/{y}/{x}.jpg via the nginx CORS proxy. The IndexedDB
-// id carries a style prefix so both styles can coexist in the cache.
+// Both are z11 {z}/{y}/{x}.jpg (y before x). ESRI answers cross-origin
+// GETs with Access-Control-Allow-Origin: *, so the standalone build needs
+// no server at all; the same-origin nginx paths are used instead when this
+// page has them (proxy cache, friendlier to the upstream). The IndexedDB id
+// carries a style prefix so both styles can coexist in the cache.
 var GROUND_STYLE_CFG = (window.CONFIG && window.CONFIG.ground &&
     window.CONFIG.ground.style) || 'streets';
 var GROUND_STYLE = GROUND_STYLE_CFG === 'satellite' ? 'satellite' : 'streets';
-var GROUND_TILE_URL = GROUND_STYLE === 'satellite' ? '/esri/imagery/' : '/esri/streets/';
+var GROUND_TILE_DIRECT = (GROUND_STYLE === 'satellite')
+    ? 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Imagery/MapServer/tile/'
+    : 'https://server.arcgisonline.com/ArcGIS/rest/services/World_Street_Map/MapServer/tile/';
+var GROUND_TILE_PROXY = (GROUND_STYLE === 'satellite') ? '/esri/imagery/' : '/esri/streets/';
+// direct by default: works from any origin, including a plain file:// open
+var GROUND_TILE_URL = GROUND_TILE_DIRECT;
 var GROUND_TILE_ID_PREFIX = GROUND_STYLE === 'satellite' ? 'sat/' : '';
 // Debug tile overlays (border + N/S + x/y labels) - off unless
 // CONFIG.tiles.debug is true.
@@ -1172,9 +1180,31 @@ window.BackgroundCache = {
     }
 };
 
+// ---- tile source selection ---------------------------------------------
+// Start from the public upstreams so the page works anywhere, then switch a
+// source over to the same-origin proxy if a probe shows it is really served
+// by our nginx (an image content-type is required, so a SPA fallback that
+// answers 200 + HTML for every path cannot hijack the switch).
+var _tileProxyChecked = false;
+function tileProbeProxy() {
+    if (_tileProxyChecked) return;
+    _tileProxyChecked = true;
+    if (location.protocol === 'file:') return;
+    function probe(path, apply) {
+        fetch(path, { method: 'HEAD' }).then(function (r) {
+            var type = (r.headers.get('Content-Type') || '').toLowerCase();
+            if (r.ok && type.indexOf('image/') === 0) {
+                apply();
+                console.log('[clouds3d] tiles: using dev proxy ' + path);
+            }
+        }, function () {});
+    }
+    probe(ELEV_TILE_PROXY + '11/0/0.png', function () { ELEV_TILE_URL = ELEV_TILE_PROXY; });
+    probe(GROUND_TILE_PROXY + GROUND_TILE_Z + '/0/0.jpg',
+        function () { GROUND_TILE_URL = GROUND_TILE_PROXY; });
+}
 function fetchTileBlob(tileX, tileY) {
-    // ESRI World_Street_Map format: {z}/{y}/{x}.jpg via local
-    // proxy. (y before x, jpg not png)
+    // ESRI World_Street_Map format: {z}/{y}/{x}.jpg (y before x, jpg not png)
     return fetch(GROUND_TILE_URL + GROUND_TILE_Z + '/' + tileY + '/' + tileX + '.jpg')
         .then(function (r) {
             if (!r.ok) throw new Error('tile http ' + r.status);
@@ -1471,7 +1501,14 @@ function recenterGroundMosaic(centerTileX, centerTileY, dLng, dPerp) {
 var ELEV_Z = 10;
 var ELEV_TILES_PER = 1 << (11 - ELEV_Z); // z11 tiles covered per DEM tile
 var ELEV_UNIT_PX = 256 / ELEV_TILES_PER;  // canvas px per z11 tile
-var ELEV_TILE_URL = '/terrarium/';
+// elevation-tiles-prod (AWS) answers cross-origin GETs with CORS, so the
+// DEM also loads without our server; /terrarium/ is preferred when present.
+var ELEV_TILE_DIRECT = 'https://s3.amazonaws.com/elevation-tiles-prod/terrarium/';
+var ELEV_TILE_PROXY = '/terrarium/';
+var ELEV_TILE_URL = ELEV_TILE_DIRECT;
+// (the probe needs both URL pairs assigned, so it runs here, not at the
+// ground-source block)
+tileProbeProxy();
 var elevCanvas = null;
 var elevCtx = null;
 var elevTexture = null;
@@ -2098,7 +2135,6 @@ var CAR_QUERIES = carCells('geo/mw11', CAR_MOTORWAY_RX, 46.8, 9.4, 50.1, 13.4, 1
 // the proxy is actually there (see opProbeProxy), otherwise they are dropped.
 var OP_PUBLIC = [
     'https://overpass-api.de/api/interpreter',
-    'https://overpass.kumi.systems/api/interpreter',
     'https://maps.mail.ru/osm/tools/overpass/api/interpreter'
 ];
 var OP_PROXY = ['/overpass/api/interpreter', '/overpass/mail/interpreter'];