Last updated: 2026-10-18

This browser extension (Chrome and Firefox) overlays your Strava heatmaps on Mapy.com. It is designed to keep your data on your own machine.

What it accesses

• Strava heatmap tiles. When you use the overlay, the extension requests heatmap image tiles from Strava's servers (*.strava.com). These requests include the Strava cookies already stored in your browser, so Strava can authenticate you — exactly as if your browser loaded them on strava.com. This is the only way to show your personalized / high-resolution heatmap.
• Your Strava athlete ID. To request your personal heatmap, the extension reads your numeric Strava athlete ID (from your existing Strava login cookie, a Strava page you're logged into, or one you enter manually). It is stored locally and used only to build your personal-heatmap tile URLs and to save routes.
• Saving a route to your Strava account (Sync to Strava). When you click Sync to Strava, the extension reads your planned route's GPX from Mapy.com and sends it to your own Strava account (strava.com), using your logged-in session, to create a private, starred route. This happens only when you click the button; the route goes to your account only — nothing is shared with the developer or anyone else.

What it stores (locally, on your device only)

• Your settings (which layers are on, opacity) — in the page's local storage.
• Your athlete ID — in the extension's own local storage (the WebExtension storage.local area).
• A cache of heatmap image tiles — in your browser's IndexedDB, to make the map fast and reduce repeated requests. You can clear it any time via the browser.

What it does NOT do

• It does not send your data, browsing activity, or Strava information to the developer or any third-party server. There are no analytics, no tracking, and no remote code.
• It only runs on Mapy.com (the mapy.com and mapy.cz domains, for the overlay) and only contacts strava.com (to fetch your heatmap tiles and — only when you click Sync to Strava — to save a route to your own account).

Permissions

• host_permissions: *://*.strava.com/* — to fetch your heatmap tiles, and to save a planned route to your own Strava account, using your logged-in session.
• cookies — to read your Strava athlete ID from your existing Strava login cookie (for the personal heatmap and route saving). Your cookies are not sent anywhere except to Strava itself.
• storage, unlimitedStorage — to keep your settings, athlete ID, and the local tile cache.
• webRequest, webRequestBlocking (Firefox only) — Firefox doesn't send your Strava cookies with the extension's own requests to Strava, so the extension adds them back to those requests only. It doesn't touch the pages you browse or any other site.

Contact

Questions or issues: open an issue at https://github.com/matejcermak/heatmapy.