
Private Puzzles appear on the main puzzles menu. Players must respond to an invitation from the puzzle creator to join a private puzzle.
A private puzzle offers users the ability to create puzzles that are available by invitation.
Private puzzles can include any of the features found in Foldit science puzzles.
Private puzzles were originally referred to as "custom contests". Foldit had long offered a more limited contests feature, which involved a limited set of puzzle templates.
The custom contests feature was introduced in a 2019 Foldit blog post. The "custom contests" feature was renamed to "private puzzles" when the new Foldit website was launched in September 2022. The old template-based contests were also dropped at that time.
The original version of private puzzles was described in Creating custom Foldit puzzles for teaching biochemistry, published in Biochemistry and Molecular Biology Education in January 2019. The paper shows the old version of the Foldit website. The current version of the website is shown here. The supplemental information for the paper contains more detail on the configuration files needed to create a private puzzle. In particular, the puzzle setup file is described in the supplemental section of the paper.
Registration
To create a private puzzle, users must first register by external email to the Foldit administrators. As stated in the blog post, the address is mail.fold.it |at| gmail.com.
Puzzle setup

A new private puzzle requires a title and a description, along with setup files and other information.
Once registered, users have access to the Private Puzzles page on the Foldit website. The "Create New" button allows creating a new private puzzle.
A minimal setup requires either a complete protein file in PDB format, or the primary structure of a protein in FASTA format.
Due to a software glitch, the file "ref2015_cart.wts" must also be included in the puzzle setup, under the "puzzle files" section. This file can be found in a stanadard Foldit installation, in the "weights" under the "cmp-database" directory.
The fields on the "create new" page include:
- title - the title of the puzzle
- description - an additional description of the puzzle
- phase - the puzzle's release status - "prerelease", "open" or "closed"
- start time - the first time the puzzle will be available
- end time - the time puzzle will expire
- puzzle files - the PDB file, weights file, and other config files
- starting structure - the optional starting structure file
The default phase of the puzzle is "prerelease", meaning the puzzle won't be available until the specified start time. The "open" phase can be used to start a puzzle immediately. The "closed" phase can be used to end a puzzle before the specified end time.
When a PDB file is specified under "puzzle files", a modified PDB file can be specified under "starting structure". The modified structure will be what players see when they open the puzzle. Foldit standalone, the non-game version of Foldit, can be used to modify a PDB file. For example, Foldit standalone can be used to convert a folded protein from a published PDB into a straight extended chain. Foldit standalone can then save the extended chain in PDB format, allowing it to be used as the "starting structure" of a puzzle.
When the necessary fields are completed, the "Create Puzzle" button creates the puzzle, making it available to Foldit players at the start time.

A completed new puzzle form. The file "example_pdb.pdb" is found under "PDB" in the Foldit standalone examples. The file "ref2015_cart.wts" is found in any recent Foldit installation, and must be included in each private puzzle due to a software glitch.
Foldit standalone
Foldit standalone is the non-game version of Foldit. It accepts the same setup files used elsewhere in Foldit. Foldit standalone can be used to create new protein poses that can form the basis of a private puzzle, as discussed above.
Several example configurations are distributed along with Foldit standalone. These configurations include:
- Density
- DNA
- FASTA
- Guide
- Ligand
- PDB
- RNA
- Template
These configurations are available as a zip file: https://fold.it/dist/external/standalone/examples.zip.
The PDB example is used in the examples shown on this page, specifically the file "example_pdb.pdb".
Invite link

The "invite link" on a private puzzle page supplies the URL necessary to play the puzzle.
After a private puzzle is created, its puzzle page on the Foldit website contains an "invite link" field. The invite link is the URL that players use to join the private puzzle. The puzzle creator can share the invite link using any means desired, for example using a Foldit private message or by external email.
Depending on how the invite link is shared, prospective players can either click on it, or copy it and paste it into a web browser. If the player is already logged into the Foldit website, the puzzle page for the private puzzle then opens. Players are otherwise prompted to log in or to create a Foldit account before joining the puzzle.
The invite link is visible on the puzzle page, so players are free to copy it and reshare it. This is probably not a concern, since the player presumably has the link already. Invite links are not specific to one player.
Players can join a puzzle while it's still in the "prerelease" phase. Players won't be able to play the puzzle until the phase changes to "open".