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The settings for a chat window can be opened with the Settings button in the upper right.


Save settings

Settings are automatically saved in Underpass for iOS, and those settings will be remembered and available every time you open Underpass. You can see all the saved chats by navigating to the "Chats" window.

Saved Chats

If you want Underpass to stop remembering a saved chat, press the Edit button in the Chats window and delete the chats you no longer need. Then press the Done button.

Edit Chats


A chat password is highly recommended. Both devices must use the same password for the chat. You can leave the password blank, but in that case the password must be left blank on the other device too. See Passwords and encryption for more information on passwords. Your password can contain any UTF-8 characters.


A chat's password is not saved along with the other settings. All passwords are stored securely in your keychain, so if you want to save the password, you need to select "Save password". Note that if you save a chat's password to the keychain but later delete the chat, Underpass will automatically delete the chat's password from the keychain too.

Chat Nicknames

You can customize the appearance of your chat by setting the window title and the screen names of the two chat partners that appear in the messages list. These nicknames are all local to your device and are never transmitted over the network.

Chat Nicknames

Each of the two names is optional. If you leave a name setting blank, then the name will not appear before messages, just a time stamp.

Your Name Optional

Your Name Optional

Port (Internet chats)

For internet chats, a port number is required. The port can be any integer between 1024 and 65535. Underpass provides a default value that you may use if you wish. See Basic concepts for more information on internet ports.


Partner's address (Internet chats)

For internet chats, entering your partner's internet address is optional, but it is required in order for you to initiate a chat with your partner. If you leave the partner's address blank, then you must select "Listen for partner" instead.

Partner's address

You can both enter an address and select "Listen for partner" to enable both partners to initiate a chat with the other.

Underpass accepts IPv4 addresses such as, IPv6 addresses such as 2001:db8:ffff:1:201:02ff:fe03:0405, and domain names such as

Partner's computer (LAN chats)

For LAN chats, selecting your partner's computer name is optional, but it is required in order for you to initiate a chat with your partner.

Partner's computer

If you don't select a partner, then you must select "Listen for partner" instead. You can both select your partner's computer and select "Listen for partner" to enable both partners to initiate a chat with the other.

Underpass automatically detects other devices on your LAN that are running Underpass and listening for chats. The menu list changes dynamically as devices join or leave the network. If you have already selected a partner, but your partner is not currently available on the LAN, then your partner's computer name will appear disabled.

Partner's computer unavailable

Listen for partner

Select "Listen for partner" to allow your partner to start a chat with you whenever Underpass is active. Underpass stops listening when it goes into the background, but it will start listening again when it becomes the frontmost app again.

In a LAN chat, when you listen for a partner, your computer name will be displayed below the switch. Your computer name then needs to be selected in your partner's Underpass settings.


In an internet chat, when you listen for a partner, you will see a link to a web site that allow you to obtain your IP address. Underpass attempts to automatically detect your IPv4 address, and if your IPv4 address is detected, it is also displayed in the settings. This works for many but not all models of router. If Underpass is unable to detect your IPv4 address, and you don't already know the address, then you can use the "What is my IP address?" link.


Your partner can use your device's IP address to start a chat if the IP address is entered in the other device's Underpass settings.

Next: Frequently Asked Questions

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