Automating Development Environments with Nix and Custom Zellij Layouts

Introduction

Setting up terminal development environments often requires repetitive manual steps: opening split panes, launching dev tools, and configuring terminal tabs. While traditional multiplexers rely on imperative shell scripts, Zellij uses declarative layout files written in KDL (KDL Document Language).

By embedding a custom Zellij KDL layout directly inside a Nix shell expression, you can generate a fully isolated, automated terminal workspace with a single command.

The full source code for this environment is available in the rosera/nix-shell-pack repository on GitHub.

The KDL Layout Definition (dev.kdl)

Zellij utilizes the KDL format to declare workspace tab templates, status bars, and split panes clean and human-readable.

Create a dev.kdl file to describe the split-pane arrangement:

layout {
    default_tab_template {
        pane size=1 borderless=true {
            plugin location="zellij:tab-bar"
        }
        children
        pane size=2 borderless=true {
            plugin location="zellij:status-bar"
        }
    }

    tab name="Go Dev" {
        pane name="Dev" size="80%" focus=true {
            command "zsh"
        }
        pane name="Build" size="20%" {
            command "zsh"
        }
    }
}

Wrapping the Layout in Nix (shell.nix)

Next, construct a shell.nix file. This Nix expression uses pkgs.writeText to read dev.kdl and pkgs.writeShellScriptBin to package a executable script (dev-zellij) that invokes Zellij directly with the custom layout file.

with import <nixpkgs> {};

let
  # External Script: Reads './dev.kdl' and embeds it as a managed Nix store path
  scriptZellijLayout = pkgs.writeText "dev.kdl" (builtins.readFile ./dev.kdl);

  # Binary Wrapper: Generates 'dev-zellij' binary executable that runs Zellij with the layout
  zellijLayout = pkgs.writeShellScriptBin "dev-zellij" ''
    ${pkgs.zellij}/bin/zellij --layout ${scriptZellijLayout}
  '';
in
pkgs.mkShell {

  name = "zellij-dev";
  nativeBuildInputs = with pkgs; [
    zellij
    zellijLayout
  ];

  LANGUAGE = "Zellij";
  VERSION  = "zellij --version";

  shellHook = ''
    # Optional: Script environment start up
    echo "Welcome to $LANGUAGE Development Environment"
    $VERSION

    # Perform Zellij Dev Layout
    exec dev-zellij
  '';
}

Running the Environment

You can spin up this development environment either from a local clone or directly from the remote repository URL.

Option 1: Running Locally

If you have cloned the repository, navigate to the development/nix-zellij directory and execute:

nix-shell

Option 2: Running Directly from GitHub

Nix enables launching the shell directly from the remote archive without needing to clone the project manually:

nix-shell https://github.com/rosera/nix-shell-pack/archive/main.tar.gz -A development.nix-zellij

Upon executing either command, Nix fetches zellij, builds the dev-zellij wrapper package, and launches the configured multi-pane layout instantly.

The Declarative Environment Lifecycle

            [ nix-shell ]
               /     \
              /       \
             v         v
    [ Zellij Package ]  [ dev.kdl Path ]
             \         /
              \       /
               v     v
       [ dev-zellij Executable ]
                 |
                 v
       [ Managed Zellij Workspace ]

1. Evaluation: nix-shell evaluates shell.nix, importing zellij and converting dev.kdl into a store path using builtins.readFile.
2. Execution: The shellHook invokes exec dev-zellij, executing zellij --layout targeting the built KDL specification.
3. Session Isolation: Exiting the panes terminates the Zellij instance clean, returning you directly back to your host shell.

Conclusion

Combining Nix with Zellij’s declarative KDL layouts makes workspace management clean, predictable, and fully reproducible. By defining tool dependencies alongside workspace layouts in code, onboarding developers to a unified terminal configuration requires only a single nix-shell command.