Term

Nvim :help pages, generated from source using the tree-sitter-vimdoc parser.

Terminal UI tui
Nvim uses a list of terminal capabilities to display its user interface (except in --embed and --headless modes). If that information is wrong, the screen may be messed up or keys may not be recognized.

Startup startup-terminal

Nvim guesses the terminal type when it starts (except in --embed and --headless modes). The $TERM environment variable is the primary hint that determines the terminal type.
terminfo E557 E558 E559 The terminfo database is used if available.
The Unibilium library (used by Nvim to read terminfo) allows you to override the system terminfo with one in $HOME/.terminfo/ directory, in part or in whole.
Building your own terminfo is usually as simple as running this as a non-superuser: 
curl -LO https://invisible-island.net/datafiles/current/terminfo.src.gz
gunzip terminfo.src.gz
tic terminfo.src
$TERM The $TERM environment variable must match the terminal you are using! Otherwise Nvim cannot know what sequences your terminal expects, and weird or sub-optimal behavior will result (scrolling quirks, wrong colors, etc.).
$TERM is also important because it is forwarded by SSH to the remote session, unlike most other environment variables.
For this terminal Set $TERM to builtin-terms ------------------------------------------------------------------------- anything libvte-based vte, vte-256color Y (e.g. GNOME Terminal) (aliases: gnome, gnome-256color) iTerm (original) iterm, iTerm.app N iTerm2 (new capabilities) iterm2, iTerm2.app Y Konsole konsole-256color N Linux virtual terminal linux, linux-256color Y PuTTY putty, putty-256color Y rxvt rxvt, rxvt-256color Y screen screen, screen-256color Y simple terminal (st) st, st-256color Y Terminal.app nsterm N tmux tmux, tmux-256color Y Windows/ConEmu conemu Y Windows/Cygwin-built Nvim cygwin Y Windows/Interix interix Y Windows/VTP console vtpcon Y Windows/legacy console win32con Y xterm or compatible xterm, xterm-256color Y
builtin-terms builtin_terms If a terminfo database is not available or there is no entry for the current terminal, Nvim will map $TERM to a builtin entry according to the above table, or "ansi" if there is no match. For example "TERM=putty-256color" will be mapped to the builtin "putty" entry. See also tui-colors.
The builtin terminfo is not combined with any external terminfo database, nor can it be used in preference to one. You can thus entirely override any omissions or out-of-date information in the builtin terminfo database by supplying an external one with entries for the terminal type.
Settings depending on terminal term-dependent-settings
If you want to set terminal-dependent options or mappings, you can do this in your init.vim. Example:
if $TERM =~ '^\(rxvt\|screen\|interix\|putty\)\(-.*\)\?$'
    set notermguicolors
elseif $TERM =~ '^\(tmux\|iterm\|vte\|gnome\)\(-.*\)\?$'
    set termguicolors
elseif $TERM =~ '^\(xterm\)\(-.*\)\?$'
    if $XTERM_VERSION != ''
        set termguicolors
    elseif $KONSOLE_PROFILE_NAME != ''
        set termguicolors
    elseif $VTE_VERSION != ''
        set termguicolors
    else
        set notermguicolors
    endif
elseif $TERM =~ ...
    ... and so forth ...
endif
scroll-region xterm-scroll-region Where possible, Nvim will use the terminal's ability to set a scroll region in order to redraw faster when a window is scrolled. If the terminal's terminfo description describes an ability to set top and bottom scroll margins, that is used.
This will not speed up scrolling in a window that is not the full width of the terminal. Xterm has an extra ability, not described by terminfo, to set left and right scroll margins as well. If Nvim detects that the terminal is Xterm, it will make use of this ability to speed up scrolling that is not the full width of the terminal.
tui-input Nvim uses libtermkey to convert terminal escape sequences to key codes. terminfo is used first, and CSI sequences not in terminfo (including extended keys a.k.a. modifyOtherKeys or "CSI u") can also be parsed. For example, when running Nvim in tmux, this makes Nvim leave Insert mode and go to the window below:
tmux send-keys 'Escape' [ 2 7 u 'C-W' j
Where 'Escape' [ 2 7 u is an unambiguous "CSI u" sequence for the <Esc> key.
The kitty keyboard protocol https://sw.kovidgoyal.net/kitty/keyboard-protocol/ is partially supported, including keypad keys in Unicode Private Use Area. For example, this sequence is recognized by Nvim as <C-kEnter>:
CSI 57414 ; 5 u
and can be used differently from <C-CR> in mappings.
tui-modifyOtherKeys tui-csiu Historically, terminal emulators could not distinguish between certain control key modifiers and other keys. For example, <C-I> and <Tab> are represented the same way, as are <Esc> and <C-[>, <CR> and <C-M>, and <NL> and <C-J>. This meant that Nvim also could not map these keys separately.
Modern terminal emulators are able to distinguish between these pairs of keys by encoding control modifiers differently. There are two common but distinct ways of doing this, known as "modifyOtherKeys" and "CSI u". Nvim supports both encoding methods and at startup will tell the terminal emulator that it understands these key encodings. If your terminal emulator supports it then this will allow you to map the key pairs listed above separately.
At startup Nvim will query your terminal to see if it supports the CSI u encoding by writing the sequence
CSI ? u CSI c
If your terminal emulator responds with
CSI ? <flags> u
this means your terminal supports the CSI u encoding and Nvim will tell your terminal to enable it by writing the sequence
CSI > 1 u
If your terminal does not support CSI u then Nvim will instead enable the "modifyOtherKeys" encoding by writing the sequence
CSI > 4 ; 2 m
When Nvim exits cleanly it will send the corresponding sequence to disable the special key encoding. If Nvim does not exit cleanly then your terminal emulator could be in a bad state. If this happens, simply run "reset".
tui-colors Nvim uses 256 colours by default, ignoring terminfo for most terminal types, including "linux" (whose virtual terminals have had 256-colour support since 4.8) and anything claiming to be "xterm". Also when $COLORTERM or $TERM contain the string "256".
Nvim similarly assumes that any terminal emulator that sets $COLORTERM to any value, is capable of at least 16-colour operation.
true-color xterm-true-color Nvim emits true (24-bit) colours in the terminal, if 'termguicolors' is set.
It uses the "setrgbf" and "setrgbb" terminfo extensions (proposed by Rüdiger Sonderfeld in 2013). If your terminfo definition is missing them, then Nvim will decide whether to add them to your terminfo definition, using the ISO 8613-6:1994/ITU T.416:1993 control sequences for setting RGB colours (but modified to use semicolons instead of colons unless the terminal is known to follow the standard).
Another convention, pioneered in 2016 by tmux, is the "Tc" terminfo extension. If terminfo has this flag, Nvim will add constructed "setrgbf" and "setrgbb" capabilities as if they had been in the terminfo definition.
If terminfo does not (yet) have this flag, Nvim will fall back to $TERM and other environment variables. It will add constructed "setrgbf" and "setrgbb" capabilities in the case of the "rxvt", "linux", "st", "tmux", and "iterm" terminal types, or when Konsole, genuine Xterm, a libvte terminal emulator version 0.36 or later, or a terminal emulator that sets the COLORTERM environment variable to "truecolor" is detected.
xterm-resize Nvim can resize the terminal display on some terminals that implement an extension pioneered by dtterm. terminfo does not have a flag for this extension. So Nvim simply assumes that (all) "dtterm", "xterm", "teraterm", "rxvt" terminal types, and Konsole, are capable of this.
tui-cursor-shape Nvim will adjust the shape of the cursor from a block to a line when in insert mode (or as specified by the 'guicursor' option), on terminals that support it. It uses the same terminfo extensions that were pioneered by tmux for this: "Ss" and "Se". Similarly, if you set the cursor highlight group with blend=100, Nvim hides the cursor through the "cvvis" and "civis" extensions.
If your terminfo definition is missing them, then Nvim will decide whether to add them to your terminfo definition, by looking at $TERM and other environment variables. For the "rxvt", "putty", "linux", "screen", "teraterm", and "iterm" terminal types, or when Konsole, a libvte-based terminal emulator, or genuine Xterm are detected, it will add constructed "Ss" and "Se" capabilities.
tui-cursor-tmux Within tmux it may appear that Nvim is not changing the cursor, but in fact it is tmux receiving instructions from Nvim to change the cursor and not knowing what to do in turn. tmux must translate what it receives from Nvim into whatever control sequence is appropriate for the host terminal. It shares a common mechanism with Nvim, of using the "Ss" and "Se" capabilities from terminfo (for the output terminal) if they are present. Unlike Nvim, if they are not in terminfo you must add them by setting "terminal-overrides" in ~/.tmux.conf .
See the tmux(1) manual page for the details of how and what to do in the tmux configuration file. It will look something like:
set -ga terminal-overrides '*:Ss=\E[%p1%d q:Se=\E[ q'
<or (alas!) for Konsole 18.07.70 or older, something more complex like:
set -ga terminal-overrides 'xterm*:\E]50;CursorShape=%?%p1%{3}%<%t%{0}%e%{1}%;%d\007'

Window size window-size

[This is about the size of the whole window Vim is using, not a window that is created with the ":split" command.]
On Unix systems, three methods are tried to get the window size:
an ioctl call (TIOCGSIZE or TIOCGWINSZ, depends on your system)
the environment variables "LINES" and "COLUMNS"
from the terminfo entries "lines" and "columns"
If everything fails a default size of 24 lines and 80 columns is assumed. If a window-resize signal is received the size will be set again. If the window size is wrong you can use the 'lines' and 'columns' options to set the correct values. See :mode.

Slow and fast terminals slow-fast-terminal

slow-terminal
If you have a slow terminal you may want to reset the 'showcmd' and 'ruler' options. The command characters and cursor positions will not be shown in the status line (which involves a lot of cursor motions and attribute changes for every keypress or movement). If the terminal scrolls very slowly, set the 'scrolljump' to 5 or so. If the cursor is moved off the screen (e.g., with "j") Vim will scroll 5 lines at a time. Another possibility is to reduce the number of lines that Vim uses with the command "z{height}<CR>".
If the characters from the terminal are arriving with more than 1 second between them you might want to set the 'timeout' and/or 'ttimeout' option. See the "Options" chapter options.
If you are using a color terminal that is slow when displaying lines beyond the end of a buffer, this is because Nvim is drawing the whitespace twice, in two sets of colours and attributes. To prevent this, use this command:
hi NonText cterm=NONE ctermfg=NONE
This draws the spaces with the default colours and attributes, which allows the second pass of drawing to be optimized away. Note: Although in theory the colours of whitespace are immaterial, in practice they change the colours of cursors and selections that cross them. This may have a visible, but minor, effect on some UIs.

Using the mouse mouse-using

mouse-mode-table mouse-overview Overview of what the mouse buttons do, when 'mousemodel' is "extend":
Normal Mode:
event position selection change action
cursor window
<LeftMouse> yes end yes <C-LeftMouse> yes end yes "CTRL-]" (2) <S-LeftMouse> yes no change yes "*" (2) <S-LeftMouse> <LeftDrag> yes start or extend (1) no <LeftDrag> <LeftRelease> yes start or extend (1) no <MiddleMouse> yes if not active no put <MiddleMouse> yes if active no yank and put <RightMouse> yes start or extend yes <A-RightMouse> yes start or extend blockw. yes <A-RightMouse> <S-RightMouse> yes no change yes "#" (2) <S-RightMouse> <C-RightMouse> no no change no "CTRL-T" <RightDrag> yes extend no <RightDrag> <RightRelease> yes extend no <RightRelease>
Insert or Replace Mode:
event position selection change action
cursor window
<LeftMouse> yes (cannot be active) yes <C-LeftMouse> yes (cannot be active) yes "CTRL-O^]" (2) <S-LeftMouse> yes (cannot be active) yes "CTRL-O*" (2) <LeftDrag> yes start or extend (1) no like CTRL-O (1) <LeftRelease> yes start or extend (1) no like CTRL-O (1) <MiddleMouse> no (cannot be active) no put register <RightMouse> yes start or extend yes like CTRL-O <A-RightMouse> yes start or extend blockw. yes <S-RightMouse> yes (cannot be active) yes "CTRL-O#" (2) <C-RightMouse> no (cannot be active) no "CTRL-O CTRL-T"
In a help window:
event position selection change action
cursor window
<2-LeftMouse> yes (cannot be active) no "^]" (jump to help tag)
When 'mousemodel' is "popup", these are different:
Normal Mode:
event position selection change action
cursor window
<S-LeftMouse> yes start or extend (1) no <A-LeftMouse> yes start or extend blockw. no <A-LeftMouse> <RightMouse> no popup menu no
Insert or Replace Mode:
event position selection change action
cursor window
<S-LeftMouse> yes start or extend (1) no like CTRL-O (1) <A-LeftMouse> yes start or extend blockw. no <RightMouse> no popup menu no
(1) only if mouse pointer moved since press (2) only if click is in same buffer
Clicking the left mouse button causes the cursor to be positioned. If the click is in another window that window is made the active window. When editing the command-line the cursor can only be positioned on the command-line. When in Insert mode Vim remains in Insert mode. If 'scrolloff' is set, and the cursor is positioned within 'scrolloff' lines from the window border, the text is scrolled.
A selection can be started by pressing the left mouse button on the first character, moving the mouse to the last character, then releasing the mouse button. You will not always see the selection until you release the button, only in some versions (GUI, Win32) will the dragging be shown immediately. Note that you can make the text scroll by moving the mouse at least one character in the first/last line in the window when 'scrolloff' is non-zero.
In Normal, Visual and Select mode clicking the right mouse button causes the Visual area to be extended. When 'mousemodel' is "popup", the left button has to be used while keeping the shift key pressed. When clicking in a window which is editing another buffer, the Visual or Select mode is stopped.
In Normal, Visual and Select mode clicking the right mouse button with the alt key pressed causes the Visual area to become blockwise. When 'mousemodel' is "popup" the left button has to be used with the alt key. Note that this won't work on systems where the window manager consumes the mouse events when the alt key is pressed (it may move the window).
double-click Double, triple and quadruple clicks are supported when the GUI is active, for Win32 and for an xterm. For selecting text, extra clicks extend the selection:
click select
double word or % match <2-LeftMouse> triple line <3-LeftMouse> quadruple rectangular block <4-LeftMouse> Exception: In a Help window a double click jumps to help for the word that is clicked on. A double click on a word selects that word. 'iskeyword' is used to specify which characters are included in a word. A double click on a character that has a match selects until that match (like using "v%"). If the match is an #if/#else/#endif block, the selection becomes linewise. For MS-Windows and xterm the time for double clicking can be set with the 'mousetime' option. For the other systems this time is defined outside of Vim. An example, for using a double click to jump to the tag under the cursor:
:map <2-LeftMouse> :exe "tag " .. expand("<cword>")<CR>
Dragging the mouse with a double click (button-down, button-up, button-down and then drag) will result in whole words to be selected. This continues until the button is released, at which point the selection is per character again.
For scrolling with the mouse see scroll-mouse-wheel.
In Insert mode, when a selection is started, Vim goes into Normal mode temporarily. When Visual or Select mode ends, it returns to Insert mode. This is like using CTRL-O in Insert mode. Select mode is used when the 'selectmode' option contains "mouse".
<MiddleRelease> <MiddleDrag> Mouse clicks can be mapped. The codes for mouse clicks are:
code mouse button normal action
<LeftMouse> left pressed set cursor position <LeftDrag> left moved while pressed extend selection <LeftRelease> left released set selection end <MiddleMouse> middle pressed paste text at cursor position <MiddleDrag> middle moved while pressed - <MiddleRelease> middle released - <RightMouse> right pressed extend selection <RightDrag> right moved while pressed extend selection <RightRelease> right released set selection end <X1Mouse> X1 button pressed - X1Mouse <X1Drag> X1 moved while pressed - X1Drag <X1Release> X1 button release - X1Release <X2Mouse> X2 button pressed - X2Mouse <X2Drag> X2 moved while pressed - X2Drag <X2Release> X2 button release - X2Release
The X1 and X2 buttons refer to the extra buttons found on some mice. The 'Microsoft Explorer' mouse has these buttons available to the right thumb. Currently X1 and X2 only work on Win32 and X11 environments.
Examples:
:noremap <MiddleMouse> <LeftMouse><MiddleMouse>
Paste at the position of the middle mouse button click (otherwise the paste would be done at the cursor position).
:noremap <LeftRelease> <LeftRelease>y
Immediately yank the selection, when using Visual mode.
Note the use of ":noremap" instead of "map" to avoid a recursive mapping. 
:map <X1Mouse> <C-O>
:map <X2Mouse> <C-I>
Map the X1 and X2 buttons to go forwards and backwards in the jump list, see CTRL-O and CTRL-I.
mouse-swap-buttons To swap the meaning of the left and right mouse buttons:
:noremap        <LeftMouse>        <RightMouse>
:noremap        <LeftDrag>        <RightDrag>
:noremap        <LeftRelease>        <RightRelease>
:noremap        <RightMouse>        <LeftMouse>
:noremap        <RightDrag>        <LeftDrag>
:noremap        <RightRelease>        <LeftRelease>
:noremap        g<LeftMouse>        <C-RightMouse>
:noremap        g<RightMouse>        <C-LeftMouse>
:noremap!        <LeftMouse>        <RightMouse>
:noremap!        <LeftDrag>        <RightDrag>
:noremap!        <LeftRelease>        <RightRelease>
:noremap!        <RightMouse>        <LeftMouse>
:noremap!        <RightDrag>        <LeftDrag>
:noremap!        <RightRelease>        <LeftRelease>
Main
Commands index
Quick reference
Startup
Window size
Slow and fast terminals
Using the mouse