FITS is released under the GNU LGPL open source license. The source code for FITS is included in the downloadable ZIP files.

The tools bundled with FITS use the following open source licenses:

• Jhove (LGPL version 2.1 or any later version)
• Exiftool (GPL version 1 or any later version; or the artistic license)
• National Library of New Zealand Metadata Extractor (Apache Public License version 2)
• DROID (BSD (new version))
• FFIdent (LGPL)
• Tika (Apache Public License version 2)
• MediaInfo (BSD-style)

The source code for each of the above tools is available on their websites.

In addition, FITS includes the following open source libraries:

• JDOM (Apache-like license, modified Apache version 1.1)
• staxmate (BSD (new version))
• stax2 (LGPL version 2.1)
• Woodstox (LGPL version 2.1)
• xercesImpl (Apache Public License version 2)
• xml-apis (Apache Public License version 2)
• xmlunit (BSD (new version))
• JNA (Dual license LGPL version 2.1 and Apache Public License version 2)

The source code for each of the above libraries is available on their websites.