Daylight Saving Checker

WHAT IT DOES

Daylight Saving Checker is a browser extension that displays detailed information about Daylight Saving Time (DST) for your local timezone. It shows whether DST is currently active or inactive, your current timezone offset from UTC, and the date and time of the next DST transition (spring forward or fall back). A live countdown shows how much time remains until the next transition, and the tool provides quick facts about DST rules. The tool is ideal for remote workers, international teams, travelers, and anyone who needs to stay aware of timezone changes that affect scheduling, meetings, and deadlines.

WHERE IT RUNS

Daylight Saving Checker runs on any webpage, overlaying a floating panel that does not interfere with page content. It operates entirely in your browser as a lightweight userscript, using JavaScript's Date object and timezone APIs for calculations. It works on any page, whether static or dynamic, with no external dependencies. All data is calculated locally—no data is ever sent to any server.

HOW TO USE

After installation, open the floating panel by clicking the extension icon. The panel instantly displays your current DST status (Active/Inactive) with a colored indicator, your current UTC offset, and your IANA timezone name if available. The "Next Transition" section shows the date and time of the upcoming DST change, with a label indicating whether it's "Spring Forward" (clocks move forward 1 hour) or "Fall Back" (clocks move backward 1 hour). A countdown timer shows the remaining time until the transition. The "Quick Facts" section provides helpful information about DST rules in the US and Europe. Click the Refresh button to manually update the display. The panel updates automatically every minute and when the browser tab becomes visible.

REAL MECHANISM — WHY THIS WORKS

Most DST tools rely on external APIs or hardcoded transition dates that can become outdated when governments change DST rules. Daylight Saving Checker uses a deterministic algorithm that calculates DST status and transitions entirely from the browser's built-in timezone data. The engine compares the timezone offset for January 1 (standard time in the northern hemisphere) and July 1 (potential DST time) to determine which offset represents DST. For the current date, it checks if the current offset matches the DST offset. To find the next transition, the engine iterates day by day (up to 2 years) looking for a day where the timezone offset changes from the previous day. When a change is found, it identifies whether it's a spring-forward (offset decreases by 60 minutes) or fall-back (offset increases by 60 minutes) transition. The countdown is calculated by subtracting the current time from the transition date. The tool also uses Intl.DateTimeFormat().resolvedOptions().timeZone to display the IANA timezone name when available. This approach ensures accurate, reliable, and fully private DST information without requiring any external services or network access.

THE PANEL

The floating panel is fully draggable and remembers its position per site, snapping to the edges of the viewport when dragged near them. You can collapse the panel to a small icon to minimize screen distraction and expand it back with a single click. The panel is resizable from the bottom-right corner, giving you more space to view DST information. Press the Escape key to close the panel instantly. The panel remains open across page navigation within the same domain, maintaining your current view state. All preferences—panel position—are saved per domain for a seamless experience.

PLEASE NOTE

Daylight Saving Checker requires the free BotGentz extension to be installed and enabled, as it relies on the cross-extension messaging API provided by BotGentz for DOM access permissions. The DST calculation uses the browser's built-in timezone data, which may vary across browsers and operating systems. The tool searches for transitions by scanning day by day; this may take a moment but is typically very fast. The displayed IANA timezone name depends on browser support. All data is calculated locally in your browser. No DST information, timezone data, or usage data are ever sent to any server. The extension does not read, store, or transmit any personal information. It only calculates and displays DST information locally at your request.