Fiolin is a platform for running various scripts that perform different tasks. For example: combining PDFs, unpacking zip files, rotating images, etc. Some of these scripts were written by the developers of the Fiolin website (i.e., first-party scripts). Other scripts were written by software developers unaffiliated with the Fiolin website (i.e., third-party scripts).
Third-party developers do not need approval from the Fiolin developers to write and share their scripts. Since the Fiolin developers do not vet these scripts, we cannot endorse any third-party script as being useful or safe. Use at your own risk.
No. Just like with first-party scripts, your files don't leave your browser. They do control the code that generates the output files though.
Fiolin cannot guarantee that third-party scripts work as advertised. Output files may or may not have the properties they say they do. To give a silly but suggestive example, a third-party script could claim to convert pngs to jpgs but actually just ignore the input file and output a picture of Rick Astley.
To minimize these sorts of risks, Fiolin does not allow third-party scripts to generate certain risky file types (e.g., exe files). If a third-party script instructs you to change the file extension of an output file, don't do it!
Links to third-party scripts look like this: fiolin.org/third-party?gh=some-user/some-repo/some-script. Links to scripts written by the Fiolin developers look like this: fiolin.org/s/some-script. Also, third-party scripts always display the github profile picture of the script author and have links to their github page.
Anyone with a github account can write a third-party script. If you want to find out who wrote a particular script, you can click on the author's github profile picture or their username.
See the developer documentation.