Every skip on the street, tracked to the day.

No map errors, and every tile “loaded”

The Console said nothing about the map; its one error, about a page transition, was unrelated. Asking the map library itself: 16 tiles on the map, all 16 marked as loaded, none from the backup map. The app believed every picture had arrived.

> const i = [...document.querySelectorAll('img.leaflet-tile')];
  ({ tilesOnMap: i.length,
     loaded: i.filter(x => x.classList.contains('leaflet-tile-loaded')).length,
     osmTiles: i.filter(x => /openstreetmap/.test(x.src)).length })
< { tilesOnMap: 16, loaded: 16, osmTiles: 0 }

A success that is really a warning

One tile request, opened up. The status is 200 OK and the file is a real PNG, but every tile is the same 2,049-byte picture, and its ETag starts with wm: a watermark. The dark map does the same, and the referring site made no difference. It only shows when you preview the image itself: Network, Img, then Preview.

REQUEST

GET https://b.basemaps.cartocdn.com/light_all/12/2038/1351.png

STATUS

200

CONTENT-TYPE

image/png

CONTENT-LENGTH

2049

ETAG

"wm-da89c20e77c1-light"

CACHE-CONTROL

public, max-age=2592000, immutable

The browser’s network log did not list the page’s own image requests, so the tile was opened at its own address and its headers read with curl. Captured 11 November 2026.

The backup waits for an error that never comes

The map server, CARTO, now needs an API key, and without one it answers with a watermark and a 200. The app already had a backup: if a tile fails, swap to OpenStreetMap. A 200 with a valid picture is not a failure, so the swap never ran.

const tile = theme === 'light' ? makeLightTile() : makeDarkTile();
tile.addTo(mapInstance);
tile.on('tileerror', () => {
    if (!mapInstance.hasLayer(tile)) return; // already swapped
    tile.removeFrom(mapInstance);
    makeOsmTile().addTo(mapInstance);
});

Saved by accident

On quicklitrack.com the maps looked fine, for the wrong reason. The site’s security policy did not list the map server, so the requests made by its offline helper, the service worker, were blocked. Those real failures tripped the backup, and OpenStreetMap appeared. Without that worker, as in local demo mode, the watermark stayed.

Failed to load resource: net::ERR_FAILED

One map source that needs no key

Both maps now use OpenStreetMap’s own tiles, credited to its contributors, and the security policy allows that server and no longer lists CARTO. The dark look is a filter on the map layer, so switching theme no longer reloads a single tile. Checked on desktop and at phone width, light and dark, with the live site’s security headers; all 45 tests pass. The lesson: a backup that waits for errors cannot catch a server that says yes.

export function createBaseTileLayer() {
    return L.tileLayer('https://tile.openstreetmap.org/{z}/{x}/{y}.png', {
        attribution: '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors',
        maxZoom: 19
    });
}

/* OSM base map, muted so the status pins carry the colour */
--map-tile-filter: saturate(0.45);

/* OSM base map, inverted to a dark map; pins sit in another pane and keep their colours */
--map-tile-filter: invert(1) hue-rotate(180deg) brightness(0.95) contrast(0.9) saturate(0.35);

.leaflet-tile-pane {
    filter: var(--map-tile-filter, none);
}

Fixed in Quicklitrack commit c86dae6, 11 November 2026. Shipping with the next release.