A telescope or lab instrument hands you a .fits file and you just want the numbers behind the image. This page reads the FITS header and structural metadata and returns them as a single JSON document.
How to convert FITS to JSON
- Upload a FITS file up to 40 MB.
- Press Convert file and review the JSON report.
What you get
A JSON object with the decoded FITS header keywords: SIMPLE, BITPIX, NAXIS, EXTEND, plus whatever your instrument wrote — OBJECT, TELESCOP, DATE-OBS, RA/DEC coordinate keywords, or custom calibration values.
Notes and limits
- FITS parsing is handled by ExifTool, the same metadata engine used to read EXIF and other scientific file formats.
- The JSON contains header keywords and structure; pixel values and table rows are not expanded.
- Files that cannot be read as FITS produce a clear error message.
- No data leaves your browser other than the file itself — it is processed in a sandbox and never stored.
When this helps
- Verifying what an instrument actually wrote into a FITS header
- Pulling observation metadata into a notebook, dashboard, or script
- Comparing headers across exposures without opening dedicated astronomy software
- Spotting malformed or truncated FITS files before processing them
Operation details
What happens: ExifTool parses the FITS primary header and extension headers, decoding keyword cards into typed JSON fields. Pixel arrays and table bodies are not exported.
Engine: ExifTool 13.55 FITS reader.
Inputs: .fits, .fit, or .fts up to 40 MB.
Output: JSON of header keywords (SIMPLE, BITPIX, NAXIS, OBJECT, DATE-OBS, custom calibration keys, etc.).
Lossy? Read-only — no image data is rewritten.
Common failures: Non-FITS files fail with a clear unsupported-format error instead of a fake report.
Use when: You need observation metadata from a telescope or lab export without installing desktop astronomy software.