BadTerm

The badass terminal.

A cross-platform BBS client (telnet, SSH, RLogin and real modems) written in Rust, in the tradition of SyncTERM, NetRunner, QModem and Telix. Runs natively on Windows, macOS and Linux. Website, help and downloads: https://badterm.com/.

BadTerm draws its own text-mode screen using real CP437 bitmap fonts, so ANSI art renders pixel-for-pixel as it did on a VGA card. It doesn't depend on the fonts and colors of a host terminal.

Status: 0.3, in daily use. Telnet, telnet over TLS, SSH, RLogin, raw TCP and modem connections; ZMODEM, YMODEM, XMODEM and Kermit transfers; ANSI-BBS (as SyncTERM's CTerm, with its fonts, sixel, pictures, sound and the mouse), Avatar, RIPscrip, PETSCII, ATASCII, Viewdata, BBC Mode 7, IGS (Atari ST) and SkyPix (Amiga); and the dialing directory with import and export all work. See ROADMAP.md for what's planned.

Features

• ANSI-BBS emulation: cursor movement, erase/insert/delete, scroll regions, save/restore cursor, cursor position reports (used by BBSes to detect ANSI), CP437 "graphic" control characters, form feed clears the screen
• Fonts: the IBM VGA fonts; the Amiga fonts (Topaz, Topaz Plus, MicroKnight, MicroKnight Plus, P0T-NOoDLE, mO'sOul) for Amiga BBSes; and SyncTERM's 31 code-page fonts (Cyrillic in CP866, KOI8-R and CP1251, Greek, Hebrew, Turkish, Baltic, Central and West European, Armenian, CP850, CP865...) for BBSes in other languages: set per directory entry, or by the BBS with CTerm's font selection (CSI n ; m SP D, including the bright and blink font slots of CSI ?31h / ?34h). With a code-page font on the screen, what you type and paste is sent in that code page (Cyrillic as CP866 or KOI8-R, say), and text you copy comes out as the characters it shows
• Palette changes from the BBS (OSC 4, reset with OSC 104), as SyncTERM does
• Colors: 16-color VGA palette with bold-as-bright, iCE colors (blink bit selects a bright background; toggle with Alt-I, or by the server with CSI ?33h), real blinking text when iCE is off, xterm 256-color, and 24-bit color (SGR 38;2 and the CTerm/PabloDraw CSI 1;r;g;b t form)
• Telnet with BINARY, ECHO, SGA, TERMINAL-TYPE and NAWS negotiation; telnet over TLS ("TelnetS", port 992); RLogin, which logs straight in with the entry's user name and password; raw TCP for systems that don't speak telnet
• A real modem: entries whose protocol is Modem dial their phone number (the entry's address) on a modem on a serial port, a USB modem, a WiFi modem or tcpser. Set the port, speed, flow control, init string and dial command once in Settings (Alt-O, the Modem tab). The modem's replies show as it dials, a BUSY line is redialed like a busy BBS, and the call ends when the carrier drops: NO CARRIER.
• SSH (pure Rust, no OpenSSL): "none" auth for BBSes that run their own login, public keys (a key file set in the entry, your SSH agent, or ~/.ssh/id_ed25519, id_ecdsa, id_rsa), keyboard-interactive and password auth. Anything not stored, such as a password, a key passphrase or a one-time code, is asked for in a login dialog. Host keys are trusted on first use and pinned in BadTerm's own known_hosts; a changed key is refused with an explanation.
• ZMODEM downloads start automatically when the BBS sends a file. Uploads start with Alt-U, by dropping files on the window, or automatically when the BBS starts receiving. Batches, progress, speed and ETA are shown, and Esc cancels. Downloads never overwrite existing files. An interrupted download is kept as name.part and resumes where it stopped when the BBS sends the file again (ZMODEM crash recovery).
• YMODEM, YMODEM-G and XMODEM (CRC, 1K or the original checksum), for BBSes and doors that offer them: start the BBS's side, then Alt-G to download or Alt-U to upload. YMODEM keeps file names and sizes and sends several files; XMODEM asks what to save a download as.
• Kermit, with long packets, sliding windows, CRC checks, compression and file sizes, as C-Kermit and G-Kermit speak it: a download starts by itself when the BBS's Kermit sends; to upload, start the BBS's Kermit receiving, then Alt-U and choose Kermit.
• A file picker for uploads: browse folders, mark several files with Space, or press Tab to type a path
• An ANSI viewer (Alt-F, badterm file.ans, or drop a file on the window when not in a call): scroll through art in its own width, font and colors, with its SAUCE title, artist, group, date and comments (I)
• CP437 and UTF-8 sessions, switchable per entry or live with Alt-E
• RIPscrip graphics, for RIPterm-era BBSes (set the entry's emulation to RIPscrip): the 640x350 EGA scenes of lines, shapes, fills, patterns and text, with the 80x43 text screen over them, and clickable buttons and mouse areas that send their commands. BadTerm answers the BBS's RIP query (ESC [ !), so the BBS knows to send them. Icons and scene files are kept in the BBS's folder of its file cache (or found in the downloads), and the BBS can ask whether you have them. Not supported: RIP's own file transfers and variables.
• Sixel graphics: pictures sent by the BBS (ESC P q) are drawn where the text cursor is, in up to 256 colors, as SyncTERM and xterm draw them. They scroll with the text, stay in the scrollback, and text written over them replaces them. BadTerm says it does sixel when asked (CTerm's attributes, ESC [ < c, and the graphics size, ESC [ ? 2 ; 1 S).
• SyncTERM's pictures, for Synchronet's graphical doors (SyncDoom and the like): BBSes can store files in a cache on your computer (a folder per BBS, in BadTerm's cache folder, at most 256 MB each) and draw PPM and JPEG XL pictures, from it or sent inline, anywhere on the screen, cropped, flipped, zoomed and masked, and copy and paste pixels. To get them, BadTerm identifies itself as CTerm (SyncTERM's emulation, revision 1.332) when a BBS asks, and says which of its features it has.
• AVATAR (AVT/0 and AVT/0+), the compact codes of Opus, Maximus and other FidoNet-era BBSes, alongside ANSI: set the entry's emulation to Avatar
• Commodore 64 (PETSCII) and Atari 8-bit (ATASCII) BBSes, set by the entry's emulation: their 40-column screens, colors, character sets (the C64's two, switched by the BBS), reverse video and screen-editor codes, and their keys (Enter, DEL, the cursor keys, the C64's F1 to F8 and RUN/STOP on Esc). The fonts are BadTerm's own, in those machines' style
• Viewdata (Prestel) BBSes, such as Telstar, set by the entry's emulation: the 40x24 teletext page in its eight colors, with mosaic block graphics (contiguous and separated, held across color changes), double height, flashing and concealed text, and the UK character set. Attributes are worked out from the page as a real decoder does, so a BBS that rewrites part of a row gets the colors right. Enter sends the # key, and Alt-K reveals concealed text (answers to quizzes, say). BBC Micro Mode 7, the BBC's teletext screen, is an emulation of its own: 40x25, attributes as bytes, a scrolling screen, the BBC's own characters and keys.
• IGS, the graphics of Atari ST BBSes (Instant Graphics and Sound, version 2.19): VT-52 text and GEM drawing on the ST's screen (medium resolution, or low with sixteen colors): lines in their styles, widths and ends, boxes, circles, ellipses, arcs and pie slices, polygons and flood fills in the VDI's fill patterns and hatches, text in its sizes and effects, markers, blits, palettes, loops and clickable mouse zones. The ST's smallest text is in a 6x6 font of BadTerm's own. Color cycling (X 8) animates as on the ST, and a key cuts it, or a pause, short. Not yet: the sound chip's effects and music, and MIDI.
• SkyPix, the graphics of Amiga BBSes (SkyLine's, then C-Net's): ANSI text in Topaz on the Amiga's 640x200 screen in 16 colors, with SkyPix's drawing commands: pixels, lines, filled rectangles, ellipses, flood fills, brushes blitted with the Amiga's minterms, palettes, text placed at any pixel, delays and mouse clicks. Amiga disk fonts are drawn as Topaz at about their size. Not yet: samples, and brushes sent by XMODEM (refused).
• Scrollback of 10,000 lines. Screens cleared by the BBS are kept, so you can scroll back through menus you've already left.
• Session capture to .ans files (Alt-C), or for an entry from the start of each call, to a file name of your choosing ({name}, {date} and {time} are filled in). A .txt capture keeps only the text, as a log.
• The bell (Ctrl-G) beeps, flashes the screen, both, or neither, set in Settings and per directory entry
• Copy with the mouse: drag to select text and it is copied when you let go; hold Shift as you let go to copy it with its colors, as ANSI
• The mouse for the BBS: a BBS or door that asks for the mouse (xterm's modes 9, 1000, 1002, 1003, 1006 and 1016, as Synchronet's doors use them) gets your clicks, drags, movement and wheel, as text cells or pixels. Hold Shift to select and copy text instead. Pasting goes in brackets (ESC [ 200 ~ ... 201 ~) when the BBS asks for that (CSI ? 2004 h).
• Fonts from the BBS: fonts a BBS sends (CTerm's loadable fonts, 8x16, 8x14 or 8x8, by DCS, the older CSI = n ; n { or from SyncTERM's cache) are used where the BBS selects them, stretched to the screen's cells if their height differs.
• Save the scrollback (Alt-S) as an .ans file for ANSI viewers and editors, or as plain .txt, or save the screen as a .png
• Dialing directory with add/edit/delete, quick connect, call counts, last-called dates, pinned favorites, search (/), sorting by name, last called or number of calls (S), and groups (G shows one at a time). Each entry can have its own download and upload folders, and can do without the status line. It starts with The Vortex BBS, the project's home BBS.
• Passwords in the OS keychain (Keychain on macOS, Credential Manager on Windows, the Secret Service on Linux) rather than the directory file. Where no keychain is available, they stay in the file.
• Import/export of SyncTERM .lst, CSV, JSON and TOML directories, and import from NetRunner, EtherTerm, MagiTerm and Qodem (fonebook.txt). Use the dialer, the command line, or drag a file onto the window.
• ANSI music: BBS tunes in the BASIC PLAY language (ESC [ N or ESC [ | up to Ctrl-N) play as PC-speaker square waves. As in BASIC and SyncTERM, a tune plays in the foreground (MF) unless the BBS says MB: what the BBS sends after it waits until it ends. Alt-M turns it off, or also on for ESC [ M, which many doors use but which otherwise means "delete a line"
• SyncTERM's sound, for Synchronet's doors: sound effects and music the BBS sends (WAV, AIFF, VOC, FLAC, MP3, and Ogg Opus or Vorbis, from the cache or inline) or has BadTerm synthesize, on 16 channels mixed together with fades, loops, crossfades and volume, as CTerm documents them. Long music is decoded in the background, so the screen doesn't wait for it. Alt-M's "off" silences these too
• Phosphor mode (Alt-P): the look of a CRT, with glowing text, scanlines and curved glass, in color or as a green or amber monochrome monitor, for every BBS or chosen per directory entry. How much the text glows, how strong the scanlines are and how curved the glass is are each set in Settings. It starts off, with crisp pixels; turned on, it is a color CRT with a light glow, medium scanlines and flat glass. BadTerm starts with 8-dot characters and square pixels, fitted to the window in its own shape
• VGA-accurate display options: 9-dot character cells, where the line-drawing characters join up as they did on a VGA (Alt-W), and the 4:3 shape of a CRT instead of square pixels (Alt-A). Entries can use 80x43, 80x50 and 132-column screen modes.
• Baud rate emulation, per entry (300 to 115200 bps): text arrives at the speed it was drawn for, so ANSI animations play as intended. ZMODEM transfers still run at full speed.
• The window: the screen fills it, keeping its shape, and when you resize the window it settles into that shape too, so there are no borders (Settings, Scaling, also offers whole-number steps for exact pixels, or stretching). Fullscreen (Alt-Enter) and maximized windows fill the screen. BadTerm opens at the size and place you left it.
• Clipboard paste (Alt-V, Shift-Ins)

Installing

Downloads are on the website and the releases page.

• Windows: run badterm-…-windows-x64-setup.exe (it and badterm.exe are code signed). It installs for you alone without administrator rights (or for everyone, if you choose), adds BadTerm to the Start menu and opens telnet://, telnets:// and rlogin:// links with it. Or unzip badterm-…-windows-x64.zip and run badterm.exe from anywhere.
• macOS: open badterm-…-macos-arm64.dmg and drag BadTerm to Applications. It is signed with an Apple Developer ID and notarized by Apple, so it opens like any other app. It opens telnet:// links once it has been run.
• Linux: install badterm-…-linux-x64.deb (Debian, Ubuntu) or badterm-…-linux-x64.rpm (Fedora, RHEL, openSUSE), for example with sudo apt install ./badterm-…-linux-x64.deb. They, the AppImage and the tarball need glibc 2.28 or newer: Debian 10, Ubuntu 20.04, RHEL 8 and later. Or use the AppImage, which runs on most distributions: chmod +x it and run it. The tarball has the bare program, plus badterm.desktop and badterm.png for adding it to your menus by hand (copy them to ~/.local/share/applications/ and ~/.local/share/icons/hicolor/256x256/apps/).

Building

Install Rust (stable, 1.89 or newer) from https://rustup.rs, then:

cargo build --release
./target/release/badterm

No extra system libraries are required on Linux: X11 and Wayland are both supported, and they and ALSA (for sound) are loaded at run time.

Usage

BadTerm opens with its splash screen for two seconds (any key skips it; Settings, General turns it off), then a start-up banner with the version, as terminal programs did.

badterm                         start, not connected (Alt-D opens the dialing directory)
badterm bbs.example.org         connect directly (also host:port,
                                 telnet://host:port, telnets://host:port,
                                 rlogin://user@host, raw://host:port,
                                 ssh://user@host:port)
badterm --import syncterm.lst   add entries from a SyncTERM, NetRunner (.phn),
                                 Qodem (fonebook.txt), MagiTerm or EtherTerm
                                 directory, a CSV list (ours, or the Telnet BBS
                                 Guide's bbslist.csv), JSON or TOML
badterm --export bbses.csv      write the directory (format from extension)
badterm --paths                 show where data is stored (settings,
                                 directory, captures, downloads, themes,
                                 bezels, known hosts, the BBS file cache)
badterm --render art.ans out.png
                                 draw an ANSI file to a PNG (add --screen for
                                 just the last 80x25 screen, --crt color|green|
                                 amber, --glow, --scanlines, --curvature, --nine-dot,
                                 --aspect, --font for Amiga art, --bezel)

On Windows, BadTerm is a GUI program, so cmd doesn't wait for it and its command-line output can appear after the next prompt. Use start /wait badterm --help in cmd, or run it from PowerShell.

Dialing directory keys

Open the dialing directory with Alt-D (Cmd-D on macOS) at any time. If you are connected, the call stays up behind it, and dialing another BBS asks before hanging up.

Hotkeys

Every client command is on Alt (on macOS, Cmd, since Option types characters there). Every Ctrl key, Ctrl-D included, always goes to the BBS.

Alt-P, Alt-A, Alt-W and Alt-M work anywhere, including in the dialing directory, and are remembered in settings.toml, as are the window's size, place (not on Wayland, which places windows itself) and whether it was maximized, for the next start. An entry's "Screen mode" can be 80x25, 80x43, 80x50, 132x25, 132x37 or 132x52 (43 lines or more in the 8x8 font), and its "Phosphor mode" can override Alt-P for that BBS. While connected to a BBS with its own phosphor mode, Alt-P changes that BBS's mode rather than the global one. Its "iCE colors" setting is Auto (the BBS turns them on with CSI ?33h, as before), On or Off; with On or Off, Alt-I changes that BBS's setting too.

Alt-O (or O in the dialing directory) opens the settings, on five tabs (Tab and Shift-Tab, or PgUp/PgDn, move between them). Folders sets where downloads, captures and saved screens go and where the upload and ANSI-art pickers start (Enter to change, Del for the default). The others: phosphor mode, its glow (off, light, medium or strong: how much bright text lights the dark around it), its scanlines (off, light, medium or strong) and the curve of its glass (off for a flat screen, slight, medium or strong), the aspect ratio, scaling (fit keeping the shape; auto, which is whole numbers in a window and fit in full screen; always whole numbers; or stretch to fill), character cells, sound and music, the bell (a beep, a flash of the screen, both or neither; an entry can have its own), redialing, the modem (see "Dialing with a modem" below), and the colors of BadTerm's own screens. Pick one of the color schemes (Midnight, the default; Classic blue, Gray windows, Green phosphor, Amber, Monochrome, Ocean, Crimson, Plum, Dark blue and Dark cyan, which have no colored backgrounds, or Bad Cluster, in the copper and teal of badcluster.dev), or, under "Edit colors", give each part of the interface (title bar, selected entry, windows, input fields, key hints, ...) its own foreground and background from a grid of the 16 x 8 combinations, as in QModem and Telix. Changes show and are saved straight away; in the grid, Esc undoes the last part.

"Keyboard macros" sets what Alt-1 to Alt-0 send, written as in Telix and QModem: ^M is Enter, ^[ Esc and ^A to ^Z the other control keys, ~ waits half a second, and {user} and {password} are the directory entry's. {user}^M~{password}^M, for example, logs in.

Color themes can be shared. "Save as a theme" writes the current colors to a file in the themes folder (badterm --paths shows where), and "Import a theme" copies someone else's file there and switches to it. Every theme in the folder is in the color scheme list. A theme is a small TOML file, easy to edit by hand; parts it leaves out keep the default colors:

name = "Sunrise"
author = "sysop"

[colors]
title_bar = { fg = "yellow", bg = "red" }
selected = { fg = "black", bg = "brown" }
window = { fg = "white", bg = "magenta" }

The colors are black, blue, green, cyan, red, magenta, brown, light gray, dark gray, light blue, light green, light cyan, light red, light magenta, yellow and white. The parts are title_bar, border, headings, entries, selected, info, help, help_key, status, status_alt, window, window_title, window_text, field_name, field_value, input, keys, note and error.

A theme can also bring its own 16 colors, in place of the VGA's, for BadTerm's screens (the BBS's keep theirs), as the Bad Cluster scheme does: palette = ["#0E1015", "#161922", ...] under [colors], sixteen #RRGGBB colors in the order above.

More themes, and more bezels, are on the website's extras page, from the extras folder here, where you can add your own.

"Monitor bezel" draws a monitor around the screen: a beige 1980s monitor, a platinum 1990s one, a charcoal late-1990s one, or a terminal (original designs, not any maker's). The picture then fills the monitor's 4:3 screen, as it did on the real thing; it looks best with phosphor mode on. For your own, put a PNG in the bezels folder, with the screen area see-through (transparent): BadTerm finds the screen from the transparent part in the middle and draws the terminal there. A photo of your own old monitor works well.

"Check for updates" is off unless you turn it on. When it is on, BadTerm asks git.badcluster.dev for the newest release once each time it starts (one HTTPS request, with nothing in it but BadTerm's version), and if there is a newer one says so on the status bar and the start screen, with a link to the website. It never downloads or installs anything itself.

Downloads are saved to Downloads/BadTerm; badterm --paths shows every location BadTerm uses.

For SSH entries, set the user name in the entry. Many BBSes accept a user like new or guest and then run their own login. BadTerm logs in with:

1. "none", which is all most BBSes need;
2. public keys: the entry's "SSH key file" (asking for its passphrase if it has one), then your SSH agent (SSH_AUTH_SOCK; on Windows the OpenSSH agent service or Pageant), then unencrypted ~/.ssh/id_ed25519, id_ecdsa and id_rsa. Encrypted default keys are skipped rather than asking for a passphrase on every BBS that offers key logins: add them to your agent, or name one in the entry;
3. keyboard-interactive or password, using the entry's password if there is one and asking otherwise (or when it is refused). The login dialog can remember the password for next time (Tab).

Entries with a user name log in by themselves over telnet (the entry's "Auto-login" setting): once the BBS pauses at a prompt such as Login:, User name: or Synchronet's NN:, BadTerm sends the user name, and then the password at Password:. It answers each once, only in the first two minutes of a call, and never sends the password before the user name. Alt-L sends them by hand instead, one press each.

A BBS that can't be reached, or that answers and hangs up straight away saying it is busy, is called again every 15 seconds, up to 10 times; Esc stops it and Alt-R calls at once. Set redial = false in settings.toml to turn this off.

Telnet over TLS checks the BBS's certificate against the usual certificate authorities. Many BBSes use self-signed certificates, so one that fails that check is trusted on first use and pinned in tls_known_hosts (beside known_hosts), and a later, different certificate is refused; so is a self-signed certificate from a BBS whose certificate an authority signed before.

RLogin sends the entry's password as the "client user name" and its user name as the "server user name", as SyncTERM does, which is how Synchronet and other BBSes log RLogin callers in.

Dialing with a modem

BadTerm dials out through a modem on a serial port, a USB modem, a WiFi modem, or anything that acts like one (tcpser, for example). In Settings, on the Modem tab, set the serial port (/dev/ttyUSB0, /dev/cu.usbmodem…, COM3; Enter types it, ← → step through the ports found), the speed between the computer and the modem, the flow control (RTS/CTS for almost every modem), the init string (ATZ, or AT&F) and the dial command (ATDT for tone, ATDP for pulse). Then give a directory entry the protocol Modem and the phone number as its address.

Calling it shows the modem's replies as it dials. BUSY, NO ANSWER and the like are redialed as a busy BBS is; the call ends when the carrier drops (DCD, or NO CARRIER where the port doesn't report it), and Alt-H drops DTR, then sends +++ and ATH0.

Emulations

An entry's "Emulation" sets how what the BBS sends is shown: CP437 (ANSI-BBS, the usual), UTF-8, Avatar (AVT/0 and AVT/0+ alongside ANSI), RIPscrip (graphics: click a button or mouse area to send its command; the text screen is 80x43 over the 640x350 graphics), PETSCII (Commodore 64: F1 to F8 are the C64's, Esc is RUN/STOP), ATASCII (Atari 8-bit), Viewdata (Prestel: Enter is the # key), Mode 7 (BBC Micro), IGS (Atari ST) or SkyPix (Amiga).

Passwords you enter in the directory, remember from the login dialog, or import with a SyncTERM list are moved into the OS keychain when the directory is saved. Exported directories don't include them.

Keys are sent the way ANSI-BBS software expects: arrows as ESC [ A..D, Home/End as ESC [ H / ESC [ K, PgUp/PgDn as ESC [ V / ESC [ U, Ins as ESC [ @ and Del as DEL. The other emulations send their own machine's keys: the C64's and Atari's codes, a Prestel keyboard's (Enter is #), the BBC Micro's (Delete is DEL, the arrows 0x88 to 0x8B), and the Atari ST's VT-52 arrows (ESC A..D).

Website

site/ holds the website: the home page, the help page and the extras page of themes and bezels (built from extras/); see site/README.md.

Project layout

crates/badterm-core   front-end independent library: CP437, screen model,
                       ANSI parser and the other emulations (RIPscrip,
                       Avatar, PETSCII, ATASCII, Viewdata, IGS, SkyPix),
                       sixel and SyncTERM's pictures and sound, telnet, SSH
                       and modems, transfers, dialing directory, sessions
crates/badterm        the windowed client (winit + softbuffer): renderer,
                       phosphor mode, the sound mixer, text-mode dialer and
                       settings
extras/               themes and bezels offered for download
site/                 the website
packaging/            installers and packages (Windows, macOS, Linux)

badterm-core has no GUI dependencies, so it can drive other front ends (a TUI, a headless bot, a test harness) as well.

Testing

cargo test

The ZMODEM interoperability tests run against lrzsz's sz and rz when they are installed (apt install lrzsz, brew install lrzsz), and the Kermit ones against C-Kermit (apt install ckermit); they are skipped otherwise. CI sets BADTERM_REQUIRE_LRZSZ=1 and BADTERM_REQUIRE_KERMIT=1 so they can't be skipped there. On Linux, a fake modem on a pseudo-terminal tests dialing. In CI on Windows and macOS, saving passwords in the OS keychain is tested too.

To render sample frames to images for visual inspection:

BADTERM_SNAPSHOT_DIR=/tmp/shots cargo test -p badterm snapshot -- --ignored

The extras' previews (and the bezels themselves) are drawn the same way; see extras/README.md.

License

Copyright (C) 2026 Bad Cluster.

BadTerm is free software, licensed under the GNU General Public License, version 3 or (at your option) any later version. See LICENSE.

The bundled VGA fonts come from DOSBox (GPL-2.0-or-later), and the Amiga fonts from TrueSchool's collection (GPL with the font exception), the code-page fonts from Synchronet's SyncTERM (LGPL-2.1-or-later); the C64, Atari and 6x6 fonts are BadTerm's own. See crates/badterm/assets/fonts/README.md and crates/badterm-core/assets/README.md. IGS's fill patterns, line styles and markers are the GEM VDI's, as EmuTOS (GPL-2.0-or-later) defines them. The website uses IBM Plex, under the SIL Open Font License (site/fonts/OFL.txt).