MT Code ships wearing its own theme, first in the library: the stock light palette paired with a charcoal-and-blue dark one. The card next to it, T3 Code, is the palette the app wears with no theme installed — T3's own light and dark pair — so the original look is one click away.
On web and desktop, open Settings → Appearance to choose a theme and follow the system appearance or stay in light or dark mode. To use different themes for light and dark mode, select the corresponding preview within each theme. Appearance preferences are saved separately on each device or browser.
On web and desktop, use Change theme in the command palette to select a theme without leaving chat. Press Cmd+Option+A on macOS or Ctrl+Alt+A on Windows/Linux to open the theme picker directly. Use Change appearance in the command palette to choose System, Light, or Dark independently of the theme. Cmd+Option+Shift+A on macOS or Ctrl+Alt+Shift+A on Windows/Linux cycles through those modes. Customize these shortcuts under Settings → Keybindings.
On mobile, open Settings → Appearance. Mobile has its own themes and text, code, and terminal preferences. It does not follow environment themes or defaults.
On Android 12 or newer, choose the Material You theme in Appearance to use colors from your wallpaper. Selecting another theme replaces those colors. Like other themes, Material You can be selected separately for light and dark appearances. Android uses Material You Layout by default unless you have turned it off in Appearance. It changes shapes, spacing, and controls independently of the selected theme.
Local day, night & weather is the shipped default. Choose Sidebar artwork in Appearance for a fixed sky instead, or Local day & night to follow only sunrise and sunset. The weather mode also follows clouds, rain, snow, fog, and storms. Both modes include dawn and dusk, and use the same soft cloud and star style as Night sky. The send button follows the selected artwork.
Search for a city or choose Use my location, which asks the device first and falls back to a lookup of your network address when the device will not say — so it still works on a machine with location services off. Approximate coordinates are stored only on that device and sent to Open-Meteo for daylight and weather. Set a location on each device where you use an automatic mode. Weather refreshes every 15 minutes while the app is visible. If location or weather is unavailable, the app keeps the last sky or shows Night sky until it can update. Clear location removes the saved coordinates.
For the running desktop app, set App icon → Match sidebar artwork to put the same sky behind the white MT mark. You can also choose a fixed sky or a separate local day/night/weather mode for the icon. This changes the running Dock or window icon, not the installed app bundle or the mobile launcher icon. With no sidebar artwork, Match sidebar artwork uses the default app icon.
The main sidebar, right panel, and terminal drawer open and close immediately by default. Move the Panel animations slider above 0 ms to add motion, up to 400 ms, unless reduced motion is enabled in your operating system. Moving between threads always snaps to the selected thread's panel state without replaying its transitions.
On web and desktop, choose Create theme to adjust a palette, or import a T3 Code or VS Code theme. The theme editor's color picker lets you select an area of the app to find the color to change. Export your theme as JSON to share it.
Environment themes and defaults come from the server serving your web app or the desktop app's main local environment. app.t3.codes and additional connections do not use them.
Select a published theme in Settings → Appearance to follow its palette as the server updates it. Duplicate makes an independent copy you can edit. A saved custom theme with the same ID takes precedence. If the server stops publishing the selected theme, T3 Code falls back to its standard theme.
Run this on the server to set a default and switch connected clients to it:
t3 theme set nightfallClients that are offline apply it when they reconnect. Each client applies the setting once;
choosing another theme afterward sticks until the next t3 theme set. Run the command again to
reapply it, even if the name is unchanged.
t3 theme clear removes the default without changing anyone's current theme. t3 theme show lists
the default and published themes.
Save a theme exported from T3 Code into ~/.t3/userdata/themes/ on the server, or the themes
directory under your custom state directory. The filename supplies the theme ID: nightfall.json
can be selected with t3 theme set nightfall. Keep the filename stable when updating its colors.
Do not use system, light, dark, or a built-in theme's ID.
For an integration that generates a palette, this shorter format also works:
{
"name": "Nightfall",
"appearance": "dark",
"canvas": "#1a1b26",
"accent": "#7aa2f7",
"colors": {
"terminalSelection": "#292e42",
"error": "#f7768e"
}
}Set appearance to light or dark and supply hex colors for canvas and accent. T3 Code
generates the rest. The optional colors overrides use the names in the theme editor's advanced
view.
Write updates to a temporary file and rename it into place so clients never read a partial theme. Invalid files are not published.