OpenAnyFile
Works
Viewing, inspecting and verifying. You get the full text content with encoding detection. File details, exact byte size and the detected signature are always shown.
How to open a .fits file
FITS files come from Telescopes, astronomy software, and the usual advice — buy the software that made it — is rarely what you need just to look inside one. This page covers what the format is and how to open it in a browser tab.
What is a .fits file?
Flexible Image Transport System is a text & markup format developed by NASA / IAU, first appearing in 1981. It is normally produced by Telescopes, astronomy software.
The astronomy standard, still endorsed by the IAU after four decades. Headers are plain 80-character ASCII cards, so you can read the observation metadata in any text editor.
| Full name | Flexible Image Transport System |
|---|---|
| File category | Text & markup |
| MIME type | image/fits |
| Magic bytes (file signature) | 53 49 4D 50 4C 45 (SIMPLE) |
| Developer | NASA / IAU |
| Introduced | 1981 |
| Usually created by | Telescopes, astronomy software |
| OpenAnyFile engine | plain text reader |
| Opens without upload | Yes — parsed locally in your browser |
Open a .fits file in your browser
OpenAnyFile routes .fits to its plain text reader, which displays the full text content with encoding detection.
- Open the OpenAnyFile opener in this browser — nothing to download or sign up for.
- Drag your .fits file onto the drop zone, click to browse for it, or paste it with Ctrl+V.
- The extension is detected and the file is handed to the plain text reader.
- Your FITS opens on its own viewer page: the full text content with encoding detection.
- Use fullscreen for a closer look, or download the file back out unchanged. Nothing is transmitted anywhere — the parsing happens in your own browser process.
What you can and cannot do with it here
Does not work
Editing and re-saving. OpenAnyFile is a reader, not an editor — for changes you still need special software or an equivalent.
No upload, and here is why that matters for {E}
Handing a .fits file to a random conversion site means handing over a copy you cannot get back. OpenAnyFile parses the file locally instead — the same way special software reads it off your disk, except the reader happens to be a web page. Nothing is transmitted, so there is nothing to leak, log or subpoena. It also means it keeps working with your Wi-Fi switched off.
Frequently asked questions about FITS files
Can I open a .fits file without installing special software?
Yes. OpenAnyFile's plain text reader runs in your browser, so you can read a FITS file with nothing installed. You get the full text content with encoding detection. For full editing you still need the original application — this is a viewer, not an editor.
How can I check a file really is a FITS file?
Look at the first bytes rather than the extension. A genuine FITS begins with 53 49 4D 50 4C 45 (SIMPLE). Opening the file in OpenAnyFile shows that signature in the file-details panel, so a file renamed to .fits by mistake is easy to spot.
Is it safe to open a FITS file online?
With OpenAnyFile, yes, because nothing is uploaded. The file is read locally through your browser's File API and never leaves your device, so there is no server copy to leak, log or retain. That matters most for the kind of file people are least willing to hand to a random converter site.
What is a .fits file, exactly?
Flexible Image Transport System — an image/fits format created by NASA / IAU since 1981. The astronomy standard, still endorsed by the IAU after four decades. Headers are plain 80-character ASCII cards, so you can read the observation metadata in any text editor.
Does the same viewer handle formats related to FITS?
Yes — the same engine also opens .dat, .srt, .cer, so you can compare related files without switching tools.
Related formats
These open with the same engine, so if you have one of these sitting next to your .fits file, it will open too: