Postilla

Markdown notes for the COSMIC™ desktop

A postilla is a note written in the margin. This one is a fork of Cedilla by Alex Marín, grown into a full notes app.

Features

• Vault of notes with folders, rename/move, external change detection, and the ability to open any existing folder as the vault
• Three layouts: editor only, editor + live preview, preview only (Ctrl+1 / Ctrl+2 / Ctrl+3, or the switcher in the header bar)
• Zen mode (F11): hides every bar and the sidebar, leaving only your text
• Clipboard: cut / copy / paste / select all from the Edit menu, the editor right-click menu or the usual shortcuts; Ctrl+V pastes images straight into the note
• Formatting: bold, italic, strikethrough, code, links, quotes, tables, lists, headings, rules, date & time stamps (Format menu, help bar, or shortcuts such as Ctrl+B, Ctrl+I, Ctrl+K, Ctrl+Shift+D)
• Outline (Ctrl+Shift+O): jump between the headings of the document
• Search in vault (Ctrl+Shift+F): full text (or regex) search across every note, open a result at the matching line
• Autosave with a configurable delay
• Export to PDF (rendered offline with the bundled Typst engine, no external service needed), to standalone HTML, or copy as HTML
• Tray icon in the panel with Show and Quit
• Word count, character count and reading time in the status bar
• Fully customizable syntax highlighting: import TextMate/Sublime .tmTheme files, COSMIC Terminal color schemes or simple RON themes, and optionally paint the editor and the whole window with the theme colors
• Frosted glass window effect with adjustable opacity and background color on COSMIC
• Typst math and Mermaid diagrams inside code blocks

Screenshots

The screenshots use the two bundled Postilla Ink and Postilla Parchment syntax themes, which paint the whole window with the colors of the logo (see Syntax highlighting themes).

Light theme	Typst math and Mermaid diagrams

Outline	Search in vault

Settings	Editor context menu

Zen mode (F11) leaves nothing but the text:

Install

From source

You need a Rust toolchain, just and a few development libraries. On Pop!_OS / Ubuntu:

sudo apt install just pkg-config libxkbcommon-dev libwayland-dev libfontconfig-dev libfreetype-dev libexpat1-dev

Run it straight from the source tree:

cargo run --release

Or build and install it system wide:

just build-release
sudo just install

Debian package

sudo apt install dpkg-dev
cargo install cargo-deb
just deb            # builds target/debian/postilla_<version>_amd64.deb
just install-deb    # builds and installs it with apt

The package installs the postilla binary, the launcher entry, icons and metainfo, and lists the shared libraries it needs as dependencies automatically.

Next to Cedilla

Postilla uses its own application id (io.github.atraxsrc.Postilla), so it can be installed and run side by side with Cedilla: it has its own config, themes folder and default vault. To work on the notes of an existing Cedilla installation, open Settings → General → Use another folder as vault and pick its vault; nothing is moved or copied. The Cedilla Flatpak keeps its vault in ~/.var/app/dev.mariinkys.Cedilla/data/dev.mariinkys.Cedilla/vault.

Syntax highlighting themes

Postilla ships the usual built-in themes (Inspired GitHub, Ocean, Mocha, Eighties, Solarized...), two themes in the colors of the logo (postilla-ink.ron and postilla-parchment.ron, import them from Settings → Appearance) and loads any theme placed in its themes folder (Settings → Appearance → Themes folder, or use Import theme…). Three formats are detected automatically:

Format	File	Notes
COSMIC Terminal color scheme	.ron	The exact files COSMIC Terminal imports and exports. The 16 ANSI colors are mapped onto syntax scopes (keywords → magenta, strings → green, functions → blue, headings → bright blue…).
Postilla theme	.ron	A flat list of named colors: keyword, string, heading, link… plus optional raw TextMate scope overrides. See resources/themes/example-postilla-theme.ron.
TextMate / Sublime theme	.tmTheme	Any theme from the Sublime Text ecosystem.

// A minimal Postilla theme
(
    name: "Mine",
    background: "#1e1e2e",
    foreground: "#cdd6f4",
    comment: "#6c7086",
    keyword: "#cba6f7",
    string: "#a6e3a1",
    heading: "#89b4fa",
    link: "#74c7ec",
    scopes: { "entity.name.function.macro": "#f5c2e7" },
)

Pick a theme for light and for dark mode independently. Turn on Use highlighter theme colors to paint the editor, the preview and the window background with the theme's own colors (great with terminal themes). The preview then takes its background, text and link colors from the theme (background, foreground and link in a Postilla theme). A fixed window color can also be set under Settings → Window.

Frosted glass

Under Settings → Window you can set the frosted glass behaviour (Follow desktop, Enabled, Disabled), the window opacity and the background color. Blur behind the window is provided by the compositor, so it needs COSMIC with blur support; on other desktops the window simply becomes translucent.

Typst and Mermaid

Code blocks with the typst or typ language render as Typst, which is handy for math and formulas, and blocks with mermaid or mmd render as Mermaid diagrams (powered by merman). Both are also rendered in PDF and HTML exports.

Acknowledgements

• Postilla is a fork of Cedilla, Copyright 2026 © Alex Marín (mariinkys), licensed under the GPL-3.0. Most of the foundation of this app is his work.
• Markdown and HTML rendering uses Frostmark by Mrmayman, adapted for libcosmic.
• "Pop Icons" by System76 is licensed under CC-SA-4.0.
• Built with libcosmic, Typst and syntect.

License

Released under the terms of the GPL-3.0. Postilla's changes are Copyright 2026 © Postilla contributors; the original work remains Copyright 2026 © Alex Marín.