Quick Start

Vesper Mosaic is a macOS desktop application that loads one URL into three synced panes at mobile, tablet, and desktop widths. This guide walks through installation and your first session in under five minutes.

1. Requirements

macOS - Apple Silicon or Intel.
No other dependencies. Mosaic uses Chromium webviews bundled with the app - it does not require Google Chrome to be installed.

2. Install Vesper Mosaic

Download the correct .dmg from the Vesper Mosaic page: the Apple Silicon build (arm64) for M-series Macs, or the Intel build for older Macs.
Open the .dmg and drag Vesper Mosaic to your Applications folder.
Launch Vesper Mosaic from your Applications folder. On first launch, macOS may show a security prompt - right-click the app in Finder and choose Open to proceed. See Troubleshooting for details.

Not sure which build to download?
Click the Apple menu → About This Mac. If the Chip line says Apple M1, M2, M3, or M4, you want the Apple Silicon build. If the Processor line names an Intel chip, you want the Intel build.

3. Load a URL

The app opens with a default URL already loaded (https://vesperapps.com/). To load something else, click the URL field at the top of the window or press Cmd+L.
Type or paste a URL and press Return. All three panes navigate together to the new address.
The three panes from left to right are Mobile (390 x 844), Desktop (1920 x 1080), and Tablet (768 x 1024). The unusual order keeps the widest viewport in the middle so it gets the most horizontal space in Fit mode.

4. Try the three view modes

Use the segmented toggle in the toolbar (or the keyboard shortcuts) to switch between modes:

Fit (Cmd+1) - default. All three panes are visible and scaled to share the available width.
100% (Cmd+2) - each pane renders at its native pixel width. The total content width usually exceeds the screen, so the window scrolls horizontally to pan across the panes.
Stack (Cmd+3) - the three panes stack vertically at full native width. Useful when you want one viewport visible at a time without leaving Mosaic.

See Viewport Modes for a deeper reference on how each mode behaves.

5. Scroll, click, and navigate

Scroll any pane with the trackpad or mouse wheel - the other two follow, anchored to the same DOM element when one is in view. Click any link in any pane and all three panes navigate to the new URL together. Use the toolbar Back and Forward buttons to step every pane through history simultaneously.

See Sync Behavior for the details and edge cases.

Next steps

Viewport Modes - the differences between Fit, 100%, and Stack.
Sync Behavior - how scroll sync, click sync, and the shared session work.
Cache & DevTools - purging the shared cache and opening DevTools.
Troubleshooting - if anything didn't work as expected.