About FITS Viewer

FITS Viewer is a free, open-source online tool for opening, exploring, and analyzing astronomical FITS images directly in your browser.

Why we built it

Opening FITS files has traditionally required installing desktop software like DS9, Aladin, or SAOImage. FITS Viewer brings the most common viewing and analysis tasks to the browser, making it easy to quickly inspect FITS data without installing anything.

Privacy first

All processing happens locally in your browser. Your FITS files are never uploaded to any server. We do not collect any data about you or your files. Your images stay completely private.

Features

• Open .fits, .fit, and .fts files including multi-HDU FITS files
• 15+ color maps including Grayscale, Heat, Viridis, Magma, and more
• Multiple stretch types: Linear, Log, Square Root, Arcsinh
• Interactive histogram with draggable cut controls
• Region selection with statistics (mean, sigma, min/max)
• Probe mode for reading individual pixel values and WCS coordinates
• FITS header viewer with keyword search
• Export images as PNG and region data as CSV
• Zoom, pan, and full keyboard shortcuts

Technology

FITS Viewer is built with Next.js, React, and TypeScript. It uses custom FITS parsing and canvas rendering. No server-side processing is used.

Open source

FITS Viewer is built with open web technologies.