diff --git a/org-clock-waybar.el b/org-clock-waybar.el
index 766b130..0ca2802 100644
--- a/org-clock-waybar.el
+++ b/org-clock-waybar.el
@@ -58,30 +58,81 @@
   :type 'string
   :group 'org-clock-waybar)
 
+(defcustom org-clock-waybar-text-function
+  nil
+  "Function to generate the title text.
+
+The function must return a single string.
+When nil, `org-clock-waybar-get-task-title' is used."
+  :type 'function
+  :group 'org-clock-waybar)
+
+(defcustom org-clock-waybar-alt-function
+  nil
+  "Function to generate the alternative text.
+
+The function must return a single string.
+When nil, `org-clock-waybar-get-task-category' is used."
+  :type 'function
+  :group 'org-clock-waybar)
+
+(defcustom org-clock-waybar-class-function
+  nil
+  "Function to generate the class.
+
+The function must either return a string, or a list of strings.
+When nil, `org-clock-waybar-get-tags' is used."
+  :type 'function
+  :group 'org-clock-waybar)
+
+(defcustom org-clock-waybar-tooltip-function
+  nil
+  "Function to generate the tooltip.
+
+The function must return a string.
+When nil, `org-clock-waybar-get-tooltip' is used."
+  :type 'function
+  :group 'org-clock-waybar)
+
+(defcustom org-clock-waybar-percentage-function
+  nil
+  "Function to generate the percentage text.
+
+When nil, the percentage text will be an empty string."
+  :type 'function
+  :group 'org-clock-waybar)
+
 (defconst org-clock-waybar-filename-coding-system
   (if (coding-system-p 'utf-8-emacs)
       'utf-8-emacs
     'emacs-mule)
   "Coding system of the file `org-clock-waybar-filename'.")
 
-(defsubst org-clock-waybar--get-task-title ()
+(defsubst org-clock-waybar-get-task-title ()
   "Get the title of TASK."
-  (when (org-clocking-p) (substring-no-properties org-clock-current-task)))
+  (if (org-clocking-p)
+      (substring-no-properties org-clock-current-task)
+    org-clock-waybar-not-clocked-in-text))
 
-(defsubst org-clock-waybar--get-task-category ()
+(defsubst org-clock-waybar-get-task-category ()
   "Get the category of TASK."
   (when (org-clocking-p) (get-text-property 0 'org-category org-clock-current-task)))
 
-(defun org-clock-waybar--get-tooltip ()
+(defun org-clock-waybar--list-of-strings-p (object)
+  "Return t if OBJECT is a list of strings."
+  (not (null (delq nil
+                   (mapcar (lambda (x) (and (stringp x) x)) object)))))
+
+(defun org-clock-waybar-get-tooltip ()
   "The default tooltip to send to waybar."
   (when (org-clocking-p)
     (let ((clocked-time (org-clock-get-clocked-time)))
       (format "%s: %s (%s)"
-              (org-clock-waybar--get-task-category)
-              (org-clock-waybar--get-task-title)
+              (org-clock-waybar-get-task-category)
+              (org-clock-waybar-get-task-title)
               (org-duration-from-minutes clocked-time)))))
 
-(defun org-clock-waybar--get-tags ()
+(defun org-clock-waybar-get-tags ()
   "Get the tags of the currently clocked-in task."
   (when (org-clocking-p)
     (save-window-excursion
@@ -94,18 +145,42 @@
 The output is in JSON format constructed in a way so Waybar can process it.
 If there is no clocked in task, alt becomes empty and text will be set to the
 value of `org-clock-waybar-not-clocked-in-text'."
-  (let* ((category (org-clock-waybar--get-task-category))
-         (title (org-clock-waybar--get-task-title))
-         (tooltip (org-clock-waybar--get-tooltip))
+  (let* ((text-func (or 'org-clock-waybar-text-function
+                         'org-clock-waybar-get-task-title))
+         (text (funcall text-func))
+         (alt-func (or 'org-clock-waybar-alt-function
+                       'org-clock-waybar-get-task-category))
+         (alt (funcall alt-func))
+         (tooltip-func (or 'org-clock-waybar-tooltip-function
+                           'org-clock-waybar-get-tooltip))
+         (tooltip (funcall tooltip-func))
+         (class-func (or 'org-clock-waybar-class-function
+                         'org-clock-waybar-get-tags))
+         (class (funcall class-func))
+         (percentage (when (fboundp 'org-clock-waybar-percentage-function)
+                       (funcall 'org-clock-waybar-percentage-function)))
          (output (json-new-object)))
-    (setq output (json-add-to-object
-                  output
-                  "text"
-                  (or title org-clock-waybar-not-clocked-in-text)))
-    (setq output (json-add-to-object output "alt" (or category "")))
+    (or (null title)
+        (stringp title)
+        (error "Title must be a string (org-clock-waybar)!"))
+    (or (null alt)
+        (stringp alt)
+        (error "Alt text must be a string (org-clock-waybar)!"))
+    (or (null tooltip)
+        (stringp tooltip)
+        (error "Tooltip must be a string (org-clock-waybar)!"))
+    (or (null class)
+        (stringp class)
+        (org-clock-waybar--list-of-strings-p class)
+        (error "Class must be a string or a list of strings (org-clock-waybar)!"))
+    (or (null percentage)
+        (stringp percentage)
+        (error "Percentage must be a string (org-clock-waybar)!"))
+    (setq output (json-add-to-object output "text" (or text "")))
+    (setq output (json-add-to-object output "alt" (or alt "")))
     (setq output (json-add-to-object output "tooltip" (or tooltip "")))
-    (setq output (json-add-to-object output "class" (or (org-clock-waybar--get-tags) "")))
-    (setq output (json-add-to-object output "percentage" ""))
+    (setq output (json-add-to-object output "class" (or class "")))
+    (setq output (json-add-to-object output "percentage" (or percentage "")))
     (json-encode output)))
 
 (defun org-clock-waybar-save-task ()