What is an Online FITS Header Editor?
The Flexible Image Transport System (FITS) is the global standard digital file format used by astronomers, observatories, and astrophotographers to store, transmit, and process astronomical images and scientific data. Every FITS file begins with a Header—a collection of 80-character standardized text records (cards) containing crucial metadata about telescope optics, camera sensor settings, observation time, target coordinates, and image dimensions.
Traditionally, inspecting or editing FITS metadata required installing heavy desktop software suites (such as SAOImage DS9, AstroImageJ, or PixInsight) or writing custom Python scripts using astropy.io.fits. Our Online FITS Header Editor provides a zero-install, lightweight, and modern browser-based alternative that allows you to inspect, modify, add, delete, and re-export FITS headers in seconds directly on any device.
Why Edit FITS Headers Online?
Fix Stacking & Calibration Errors
Astrophotography stacking software (such as Siril, DeepSkyStacker, and Astro Pixel Processor) requires accurate metadata. If your acquisition program recorded an incorrect filter name (FILTER), exposure time (EXPTIME), or camera gain (GAIN), files may be sorted into the wrong stacking groups or rejected during calibration.
Resolve Plate Solving Failures
Blind solving and plate solving tools (like ASTAP, PS2, and N.I.N.A) rely on telescope focal length (FOCALLEN), sensor pixel size (PIXSIZE1/XPIXSZ), and estimated coordinates (RA/DEC). Correcting these missing or mismatched values enables smooth plate solving and astrometric calibration.
Restore Bayer Color Matrices
One-shot color (OSC) astronomical cameras store raw sensor grids that require debayering. If the BAYERPAT keyword (e.g., RGGB, BGGR) is missing or corrupted, stacking tools cannot reconstruct natural color balances. You can quickly add or adjust the Bayer pattern here.
Clean Metadata & Data Archiving
Standardize target names (OBJECT), observer credits (OBSERVER), and custom comments before sharing your raw captures with astronomical databases, collaborative projects, or astrophotography communities.
How to View, Edit & Export FITS Headers
Open Your FITS File
Drag and drop any .fits, .fit, or .fts file into the upload zone above, or click to choose from your device. You can also click Load Sample FITS to test the editor immediately.
Search, Filter & Edit Keywords
Browse through the interactive table. Use the search bar to locate specific tags or filter by category (Target, Camera/Optics, WCS). Click on any value or comment to edit directly in place.
Add New Keywords or Use Quick Helpers
Click Add Keyword to create new metadata cards, or click any of the Quick Helpers (such as + OBJECT or + BAYERPAT) to instantly insert or update essential parameters.
Save & Download Updated File
Click Save & Download FITS to generate a compliant, updated FITS file. You can also export the header standalone as structured JSON or plain text TXT.
Common Astronomical FITS Keywords Reference
| Keyword | Type | Description | Example |
|---|---|---|---|
OBJECT | String | Name of the observed astronomical target | 'M31 Andromeda' |
EXPTIME | Number | Total exposure duration in seconds | 300.0 |
FILTER | String | Optical filter used during capture | 'Ha 3nm', 'Luminance' |
BAYERPAT | String | Bayer color matrix arrangement for OSC sensors | 'RGGB', 'GRBG' |
FOCALLEN | Number | Effective focal length of the telescope/lens in mm | 1050.0 |
PIXSIZE1 / XPIXSZ | Number | Physical pixel width in micrometers (microns) | 3.76 |
GAIN | Number | Sensor electronic gain setting | 100 |
CCD-TEMP | Number | Sensor cooler temperature in degrees Celsius | -10.0 |
DATE-OBS | String | UTC observation start timestamp (ISO 8601) | '2026-08-31T20:45:00' |
RA / DEC | Number | Right Ascension and Declination in degrees | 10.6847, 41.2687 |
100% Client-Side Privacy & High Performance
Astronomical FITS images commonly range from 50 MB to over 150 MB per sub-exposure. Uploading large multi-gigabyte sets over network connections to a remote server is slow and raises privacy concerns for unpublished scientific observations.
Our tool operates entirely inside your local web browser via HTML5 File and Blob APIs:
- Zero Server Uploads: Your files never leave your computer, ensuring absolute privacy and data security.
- Instant Processing: Reading headers and generating modified FITS files happens in milliseconds, regardless of file size.
- Lossless Precision: The editor strictly replaces the 2880-byte padded ASCII header block while preserving 100% of the raw binary image data without any compression or alteration.
Frequently Asked Questions (FAQ)
Is this online FITS header editor completely free?
Yes. It is 100% free to use with no subscription, no usage limits, no watermarks, and no account registration required. All operations run directly in your browser.
What operating systems and devices are supported?
Our FITS Header Editor is 100% web-based and runs seamlessly on all modern devices and platforms without any downloads or plugin requirements:
- Apple Mac & macOS: MacBook Pro, MacBook Air, iMac, Mac Studio, Mac mini (Safari, Chrome, Firefox, Edge).
- Apple iOS & iPadOS: iPhone, iPad, and iPad Pro (Safari, Chrome).
- Windows: Windows 11, 10, 8, 7 (Chrome, Edge, Firefox, Brave, Opera).
- Linux & ChromeOS: Ubuntu, Debian, Fedora, Arch Linux, Chromebooks.
- Android: Smartphones and tablets (Chrome, Samsung Internet, Firefox).
Does editing the header degrade or compress image quality?
No. FITS files separate metadata (ASCII text header) from binary pixel arrays. When you save your file, the editor only updates the header block and appends the original raw binary pixel stream untouched. There is zero compression, re-encoding, or quality loss.
Which file extensions are supported?
The editor supports all standard FITS file extensions including .fits, .fit, and .fts.
Why are some keywords locked from deletion?
Keywords such as SIMPLE, BITPIX, NAXIS, NAXIS1, and NAXIS2 define the core structural dimensions and bit depth of the dataset. Modifying or deleting them would make the FITS file unreadable by standard astronomical software.
Can I export the header without downloading the entire image?
Yes. You can click Export JSON to download a structured JSON key-value map, Export TXT to save the 80-column raw card stream, or Copy Raw Header to copy all text to your clipboard.