diff --git a/env.go b/env.go
new file mode 100644
index 0000000..b7f8066
--- /dev/null
+++ b/env.go
@@ -0,0 +1,37 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// isReadonly reports whether the editor should open in read-only mode.
+func isReadonly() bool {
+	return os.Getenv("READONLY") == "true"
+}
+
+// fixedPitchEnabled reports whether the user opted into a monospace
+// (programmer) font. The value comes from the TINY_ENCRYPT_ENABLE_FIXED_PITCH
+// environment variable; when that is unset it falls back to the file at
+// ~/.config/envs/TINY_ENCRYPT_ENABLE_FIXED_PITCH (content trimmed). The values
+// true/on/yes/1 are accepted, case-insensitively.
+func fixedPitchEnabled() bool {
+	v := os.Getenv("TINY_ENCRYPT_ENABLE_FIXED_PITCH")
+	if v == "" {
+		home, err := os.UserHomeDir()
+		if err != nil {
+			return false
+		}
+		data, err := os.ReadFile(filepath.Join(home, ".config", "envs", "TINY_ENCRYPT_ENABLE_FIXED_PITCH"))
+		if err != nil {
+			return false
+		}
+		v = strings.TrimSpace(string(data))
+	}
+	switch strings.ToLower(v) {
+	case "true", "on", "yes", "1":
+		return true
+	}
+	return false
+}
diff --git a/main.go b/main.go
index 20f3e73..3990075 100644
--- a/main.go
+++ b/main.go
@@ -4,12 +4,9 @@ import (
 	"crypto/aes"
 	"crypto/cipher"
 	"encoding/hex"
-	"encoding/json"
 	"fmt"
 	"image/color"
 	"os"
-	"path/filepath"
-	"strings"
 
 	"fyne.io/fyne/v2"
 	"fyne.io/fyne/v2/app"
@@ -24,11 +21,6 @@ const (
 	Title              = "Secure Editor"
 	AlgorithmAes256Gcm = "aes-256-gcm"
 
-	DefaultWindowWidth  = 800.0
-	DefaultWindowHeight = 600.0
-
-	ConfigFileName = "secure-editor-go-config.json"
-
 	// Exit codes:
 	//   0 -> file was saved and the editor exited
 	//   2 -> editor closed without saving
@@ -86,106 +78,6 @@ func showErrorMessage(err error, parent fyne.Window) {
 	dialog.ShowError(err, parent)
 }
 
-func isReadonly() bool {
-	return os.Getenv("READONLY") == "true"
-}
-
-// fixedPitchEnabled reports whether the user opted into a monospace
-// (programmer) font. The value comes from the TINY_ENCRYPT_ENABLE_FIXED_PITCH
-// environment variable; when that is unset it falls back to the file at
-// ~/.config/envs/TINY_ENCRYPT_ENABLE_FIXED_PITCH (content trimmed). The values
-// true/on/yes/1 are accepted, case-insensitively.
-func fixedPitchEnabled() bool {
-	v := os.Getenv("TINY_ENCRYPT_ENABLE_FIXED_PITCH")
-	if v == "" {
-		home, err := os.UserHomeDir()
-		if err != nil {
-			return false
-		}
-		data, err := os.ReadFile(filepath.Join(home, ".config", "envs", "TINY_ENCRYPT_ENABLE_FIXED_PITCH"))
-		if err != nil {
-			return false
-		}
-		v = strings.TrimSpace(string(data))
-	}
-	switch strings.ToLower(v) {
-	case "true", "on", "yes", "1":
-		return true
-	}
-	return false
-}
-
-// windowConfig is persisted to ~/.cache/secure-editor-go-config.json so the
-// editor remembers its window size across runs.
-type windowConfig struct {
-	Width  float32 `json:"width"`
-	Height float32 `json:"height"`
-}
-
-func configPath() (string, error) {
-	home, err := os.UserHomeDir()
-	if err != nil {
-		return "", err
-	}
-	return filepath.Join(home, ".cache", ConfigFileName), nil
-}
-
-func defaultConfig() windowConfig {
-	return windowConfig{Width: DefaultWindowWidth, Height: DefaultWindowHeight}
-}
-
-func loadConfig() windowConfig {
-	p, err := configPath()
-	if err != nil {
-		return defaultConfig()
-	}
-	data, err := os.ReadFile(p)
-	if err != nil {
-		return defaultConfig()
-	}
-	var c windowConfig
-	if err := json.Unmarshal(data, &c); err != nil {
-		return defaultConfig()
-	}
-	if c.Width <= 0 || c.Height <= 0 {
-		return defaultConfig()
-	}
-	return c
-}
-
-func saveConfig(size fyne.Size) {
-	p, err := configPath()
-	if err != nil {
-		return
-	}
-	if err := os.MkdirAll(filepath.Dir(p), 0755); err != nil {
-		return
-	}
-	c := windowConfig{Width: size.Width, Height: size.Height}
-	data, err := json.MarshalIndent(c, "", "  ")
-	if err != nil {
-		return
-	}
-	_ = os.WriteFile(p, data, 0644)
-}
-
-// clampToScreen shrinks size so it never exceeds the visible desktop area.
-// When the desktop size can't be determined it returns size unchanged.
-func clampToScreen(size fyne.Size) fyne.Size {
-	sw, sh := desktopSize()
-	if sw <= 0 || sh <= 0 {
-		return size
-	}
-	w, h := size.Width, size.Height
-	if w > sw {
-		w = sw
-	}
-	if h > sh {
-		h = sh
-	}
-	return fyne.NewSize(w, h)
-}
-
 // lightEditorTheme forces a light variant with a pure white input background
 // so the editable text area reads as a white editing surface regardless of
 // the system appearance setting. Readonly mode keeps the default theme (grey).
diff --git a/window.go b/window.go
new file mode 100644
index 0000000..34d52ca
--- /dev/null
+++ b/window.go
@@ -0,0 +1,87 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+
+	"fyne.io/fyne/v2"
+)
+
+const (
+	DefaultWindowWidth  = 800.0
+	DefaultWindowHeight = 600.0
+
+	ConfigFileName = "secure-editor-go-config.json"
+)
+
+// windowConfig is persisted to ~/.cache/secure-editor-go-config.json so the
+// editor remembers its window size across runs.
+type windowConfig struct {
+	Width  float32 `json:"width"`
+	Height float32 `json:"height"`
+}
+
+func configPath() (string, error) {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(home, ".cache", ConfigFileName), nil
+}
+
+func defaultConfig() windowConfig {
+	return windowConfig{Width: DefaultWindowWidth, Height: DefaultWindowHeight}
+}
+
+func loadConfig() windowConfig {
+	p, err := configPath()
+	if err != nil {
+		return defaultConfig()
+	}
+	data, err := os.ReadFile(p)
+	if err != nil {
+		return defaultConfig()
+	}
+	var c windowConfig
+	if err := json.Unmarshal(data, &c); err != nil {
+		return defaultConfig()
+	}
+	if c.Width <= 0 || c.Height <= 0 {
+		return defaultConfig()
+	}
+	return c
+}
+
+func saveConfig(size fyne.Size) {
+	p, err := configPath()
+	if err != nil {
+		return
+	}
+	if err := os.MkdirAll(filepath.Dir(p), 0755); err != nil {
+		return
+	}
+	c := windowConfig{Width: size.Width, Height: size.Height}
+	data, err := json.MarshalIndent(c, "", "  ")
+	if err != nil {
+		return
+	}
+	_ = os.WriteFile(p, data, 0644)
+}
+
+// clampToScreen shrinks size so it never exceeds the visible desktop area.
+// When the desktop size can't be determined it returns size unchanged.
+func clampToScreen(size fyne.Size) fyne.Size {
+	sw, sh := desktopSize()
+	if sw <= 0 || sh <= 0 {
+		return size
+	}
+	w, h := size.Width, size.Height
+	if w > sw {
+		w = sw
+	}
+	if h > sh {
+		h = sh
+	}
+	return fyne.NewSize(w, h)
+}