diff --git a/src/main/java/com/booleanuk/core/TodoList.java b/src/main/java/com/booleanuk/core/TodoList.java
index 675adaf0b..37d596325 100644
--- a/src/main/java/com/booleanuk/core/TodoList.java
+++ b/src/main/java/com/booleanuk/core/TodoList.java
@@ -1,5 +1,88 @@
 package com.booleanuk.core;
 
+import javax.swing.*;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
 public class TodoList {
+    List<Task> todoList;
+
+    public TodoList(){
+        this.todoList = new ArrayList<>();
+    }
+
+    public static class Task {
+        String task;
+        String status;
+
+        public Task(String task, String status){
+            this.task = task;
+            this.status = status;
+        }
+    }
+
+    public boolean addTask(String task){
+        if (task.isEmpty() || !task.matches("[a-zA-Z]+"))
+            return false;
+        else {
+            todoList.add(new Task(task, "incomplete"));
+            return true;
+        }
+    }
+
+    public List<Task> seeTodoList(){
+        return (todoList.isEmpty()) ? null : todoList;
+    }
+
+    public Task setStatus(String task, String status){
+
+        List<Task> targets = todoList.stream().filter(it -> it.task.equals(task)).toList();
+        Task updatedTask = new Task(task, status);
+        if (targets.isEmpty())
+            return null;
+        else {
+            this.todoList.set(todoList.indexOf(targets.getFirst()), updatedTask);
+            return updatedTask;
+        }
+    }
+
+    public List<Task> getCompleteTasks() {
+        List<Task> completedTasks = todoList.stream().filter(it -> it.status.equals("complete")).toList();
+        return completedTasks.isEmpty() ? null : completedTasks;
+    }
+
+    public List<Task> getIncompleteTasks() {
+        List<Task> completedTasks = todoList.stream().filter(it -> it.status.equals("incomplete")).toList();
+        return completedTasks.isEmpty() ? null : completedTasks;
+    }
+
+    public Task searchForTask(String task) {
+        List<Task> targets = todoList.stream().filter(it -> it.task.equals(task)).toList();
+        return (targets.isEmpty()) ? null : targets.getFirst();
+    }
+
+    public boolean removeTask(String task) {
+        List<Task> targets = todoList.stream().filter(it -> it.task.equals(task)).toList();
+        if (targets.isEmpty())
+            return false;
+        else {
+            todoList.remove(targets.getFirst());
+            return true;
+        }
+    }
+
+    public List<Task> seeTasksInAscendingAndAlphabeticalOrder() {
+        List<Task> res = new ArrayList<>(todoList);
+        res.sort(Comparator.comparing(s -> s.task));
+        return res.isEmpty() ? null : res;
+    }
+
+    public List<Task> seeTasksInDescendingAndAlphabeticalOrder() {
+        List<Task> res = new ArrayList<>(todoList);
+        res.sort((s1, s2) -> s2.task.compareTo(s1.task));
+        return res.isEmpty() ? null : res;
+    }
+
 
 }
diff --git a/src/main/java/com/booleanuk/core/domain-models.md b/src/main/java/com/booleanuk/core/domain-models.md
new file mode 100644
index 000000000..d3d36019c
--- /dev/null
+++ b/src/main/java/com/booleanuk/core/domain-models.md
@@ -0,0 +1,84 @@
+
+
+
+
+
+
+
+1. Add tasks to my todo list.
+
+| Classes    | Methods                        | Scenario                   | Outputs |
+|------------|--------------------------------|----------------------------|---------|
+| `TodoList` | `boolean addTask(String task)` | If task is null or invalid | false   |
+|            |                                | If task is provided        | true    |
+
+
+2. See all the tasks in my todo list.
+
+
+| Classes    | Methods                    | Scenario             | Outputs    |
+|------------|----------------------------|----------------------|------------|
+| `TodoList` | `List<Task> seeTodoList()` | If list is empty     | null       |
+|            |                            | If list is not empty | List<Task> |
+
+
+3. Change the status of a task between incomplete and complete.
+
+| Classes    | Methods                                      | Scenario                     | Outputs |
+|------------|----------------------------------------------|------------------------------|---------|
+| `TodoList` | `Task setStatus(String task, String status)` | If status or task is invalid | null    |
+|            |                                              | If status and task is valid  | Task    |
+
+
+4. Get only the complete tasks.
+
+
+| Classes    | Methods                         | Scenario                     | Outputs    |
+|------------|---------------------------------|------------------------------|------------|
+| `TodoList` | `List<Task> getCompleteTasks()` | If no tasks are complete     | null       |
+|            |                                 | If there are completed tasks | List<Task> |
+
+
+5. Get only the incomplete tasks.
+
+
+| Classes    | Methods                           | Scenario                      | Outputs    |
+|------------|-----------------------------------|-------------------------------|------------|
+| `TodoList` | `List<Task> getIncompleteTasks()` | If no tasks are incomplete    | null       |
+|            |                                   | If there are incomplete tasks | List<Task> |
+
+
+6. Search for a task and receive a message that says it wasn't found if it doesn't exist.
+
+
+| Classes    | Methods                           | Scenario              | Outputs                                   |
+|------------|-----------------------------------|-----------------------|-------------------------------------------|
+| `TodoList` | `Task searchForTask(String task)` | If task doesn't exist | print "not found" message and return null |
+|            |                                   | If task exists        | return task                               |
+
+
+7. Remove tasks from my list.
+
+
+| Classes    | Methods                           | Scenario              | Outputs                |
+|------------|-----------------------------------|-----------------------|------------------------|
+| `TodoList` | `boolean removeTask(String task)` | If task doesn't exist | false                  |
+|            |                                   | If task does exist    | remove and return true |
+
+
+8. See all the tasks in my list ordered alphabetically in ascending order.
+
+
+| Classes    | Methods                                               | Scenario                  | Outputs    |
+|------------|-------------------------------------------------------|---------------------------|------------|
+| `TodoList` | `List<Task> seeTasksInAscendingAndAlpabeticalOrder()` | If list of tasks is empty | null       |
+|            |                                                       | If list is not empty      | List<Task> |
+
+
+9. See all the tasks in my list ordered alphabetically in descending order.
+
+
+| Classes    | Methods                                                 | Scenario                  | Outputs    |
+|------------|---------------------------------------------------------|---------------------------|------------|
+| `TodoList` | `List<Task> seeTasksInDescendingAndAlphabeticalOrder()` | If list of tasks is empty | null       |
+|            |                                                         | If list is not empty      | List<Task> |
\ No newline at end of file
diff --git a/src/main/java/com/booleanuk/extension/TodoListExtension.java b/src/main/java/com/booleanuk/extension/TodoListExtension.java
new file mode 100644
index 000000000..0c70ee11b
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/TodoListExtension.java
@@ -0,0 +1,64 @@
+package com.booleanuk.extension;
+
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.List;
+
+public class TodoListExtension {
+    List<TaskExt> todoList;
+
+    public TodoListExtension() {
+        this.todoList = new ArrayList<>();
+    }
+
+    public static class TaskExt {
+        String task;
+        String status;
+        int id;
+        LocalDateTime timeCreated;
+
+        public TaskExt(String task, int id) {
+            this.task = task;
+            this.status = "incomplete";
+            this.id = id;
+            this.timeCreated = LocalDateTime.now();
+        }
+    }
+
+    public void addTaskExt(String task, int id){
+        todoList.add(new TaskExt(task, id));
+    }
+
+    public TaskExt getTaskByUniqueId(int id){
+        List<TaskExt> res = todoList.stream().filter(it -> it.id == id).toList();
+        return res.isEmpty() ? null : res.getFirst();
+    }
+
+    public TaskExt updateNameBasedOnId(int id, String task){
+        List<TaskExt> targets = todoList.stream().filter(it -> it.id == id).toList();
+        TaskExt updatedTask = new TaskExt(task, id);
+        if (targets.isEmpty())
+            return null;
+        else {
+            this.todoList.set(todoList.indexOf(targets.getFirst()), updatedTask);
+            return updatedTask;
+        }
+    }
+
+    public TaskExt updateStatusBasedOnId(int id, String newStatus) {
+        List<TaskExt> targets = todoList.stream().filter(it -> it.id == id).toList();
+        TaskExt updatedTask = new TaskExt(targets.getFirst().task, id);
+        updatedTask.status = newStatus;
+        if (targets.isEmpty())
+            return null;
+        else {
+            this.todoList.set(todoList.indexOf(targets.getFirst()), updatedTask);
+            return updatedTask;
+        }
+    }
+
+    public LocalDateTime whenTaskCreated(int id) {
+        List<TaskExt> targets = todoList.stream().filter(it -> it.id == id).toList();
+        return targets.isEmpty() ? null : targets.getFirst().timeCreated;
+    }
+}
diff --git a/src/test/java/com/booleanuk/core/TodoListTest.java b/src/test/java/com/booleanuk/core/TodoListTest.java
index 0bef779a4..ae2a233f4 100644
--- a/src/test/java/com/booleanuk/core/TodoListTest.java
+++ b/src/test/java/com/booleanuk/core/TodoListTest.java
@@ -4,10 +4,200 @@
 import org.junit.jupiter.api.Test;
 
 class TodoListTest {
+
+    @Test
+    public void testAddTasksValidInput() {
+        TodoList todoList = new TodoList();
+
+        String task1 = "running";
+        String task2 = "clean";
+
+        boolean res1 = todoList.addTask(task1);
+        boolean res2 = todoList.addTask(task2);
+
+        Assertions.assertTrue(res1);
+        Assertions.assertTrue(res2);
+    }
+
+    @Test
+    public void testAddTasksInvalidInput() {
+        TodoList todoList = new TodoList();
+
+        String task1 = "/clean!";
+        String task2 = "";
+        String task3 = "1111";
+
+        boolean res1 = todoList.addTask(task1);
+        boolean res2 = todoList.addTask(task2);
+        boolean res3 = todoList.addTask(task3);
+
+        Assertions.assertFalse(res1);
+        Assertions.assertFalse(res2);
+        Assertions.assertFalse(res3);
+    }
+
+    @Test
+    public void testSeeTodoList() {
+        TodoList todoList1 = new TodoList();
+        TodoList todoList2 = new TodoList();
+
+        String task1 = "running";
+        String task2 = "clean";
+
+        todoList1.addTask(task1);
+        todoList1.addTask(task2);
+
+        Assertions.assertNull(todoList2.seeTodoList());
+        Assertions.assertEquals(2, todoList1.seeTodoList().size());
+    }
+
+    @Test
+    public void testSetStatus() {
+        TodoList todoList = new TodoList();
+        TodoList todoList2 = new TodoList();
+
+        String task1 = "running";
+
+        todoList.addTask(task1);
+        TodoList.Task task = todoList.setStatus(task1, "complete");
+
+        Assertions.assertEquals("complete", task.status);
+        Assertions.assertNull(todoList2.setStatus(task1, "complete"));
+    }
+
+    @Test
+    public void testGetCompleteTasks() {
+        TodoList todoList = new TodoList();
+        TodoList todoList2 = new TodoList();
+
+        String task1 = "running";
+        String task2 = "cleaning";
+        String task3 = "shopping";
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        todoList2.addTask(task1);
+        todoList2.addTask(task2);
+        todoList2.addTask(task3);
+
+        todoList.setStatus(task1, "complete");
+        todoList.setStatus(task2, "complete");
+
+        Assertions.assertNull(todoList2.getCompleteTasks());
+        Assertions.assertEquals(2, todoList.getCompleteTasks().size());
+    }
+
+    @Test
+    public void testGetIncompleteTasks() {
+        TodoList todoList = new TodoList();
+
+        String task1 = "running";
+        String task2 = "cleaning";
+        String task3 = "shopping";
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        Assertions.assertEquals(3, todoList.getIncompleteTasks().size());
+
+        todoList.setStatus(task1, "complete");
+        todoList.setStatus(task2, "complete");
+        todoList.setStatus(task3, "complete");
+
+        Assertions.assertNull(todoList.getIncompleteTasks());
+    }
+
+    @Test
+    public void testSearchForTask() {
+        TodoList todoList = new TodoList();
+
+        String task1 = "running";
+        String task2 = "cleaning";
+        String task3 = "shopping";
+        String task4 = "something";
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+
+        TodoList.Task res = todoList.searchForTask(task1);
+
+        Assertions.assertEquals("running", res.task);
+        Assertions.assertEquals("incomplete", res.status);
+        Assertions.assertNull(todoList.searchForTask(task4));
+    }
+
+    @Test
+    public void testRemoveTask() {
+        TodoList todoList = new TodoList();
+
+        String task1 = "running";
+        String task2 = "shopping";
+
+        Assertions.assertFalse(todoList.removeTask(task1));
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+
+        Assertions.assertTrue(todoList.removeTask(task1));
+        Assertions.assertTrue(todoList.removeTask(task2));
+        Assertions.assertTrue(todoList.todoList.isEmpty());
+    }
+
+    @Test
+    public void testSeeTasksInAscendingAndAlphabeticalOrder() {
+
+        TodoList todoList = new TodoList();
+
+        String task1 = "running";
+        String task2 = "cleaning";
+        String task3 = "shopping";
+        String task4 = "anything";
+
+        Assertions.assertNull(todoList.seeTasksInAscendingAndAlphabeticalOrder());
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+        todoList.addTask(task4);
+
+        // Check if the list is unsorted
+        Assertions.assertEquals(task1, todoList.todoList.getFirst().task);
+
+        // Then check if the return-value of the method is correctly sorted
+        Assertions.assertEquals(task4, todoList.seeTasksInAscendingAndAlphabeticalOrder().getFirst().task);
+
+        // Then make sure the original list is unchanged
+        Assertions.assertEquals(task1, todoList.todoList.getFirst().task);
+    }
+
     @Test
-    public void exampleTest() {
-        String hello = "Hello";
-        Assertions.assertEquals("Hello", hello);
-        Assertions.assertNotEquals("Goodbye", hello);
+    public void testSeeTasksInDescendingAndAlphabeticalOrder() {
+
+        TodoList todoList = new TodoList();
+
+        String task1 = "running";
+        String task2 = "cleaning";
+        String task3 = "shopping";
+        String task4 = "anything";
+
+        Assertions.assertNull(todoList.seeTasksInDescendingAndAlphabeticalOrder());
+
+        todoList.addTask(task1);
+        todoList.addTask(task2);
+        todoList.addTask(task3);
+        todoList.addTask(task4);
+
+        // Check if the list is unsorted
+        Assertions.assertEquals(task1, todoList.todoList.getFirst().task);
+
+        // Then check if the return-value of the method is correctly sorted
+        Assertions.assertEquals(task3, todoList.seeTasksInDescendingAndAlphabeticalOrder().getFirst().task);
+
+        // Then make sure the original list is unchanged
+        Assertions.assertEquals(task1, todoList.todoList.getFirst().task);
     }
 }
diff --git a/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java b/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java
new file mode 100644
index 000000000..13b6ba000
--- /dev/null
+++ b/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java
@@ -0,0 +1,74 @@
+package com.booleanuk.extension;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDateTime;
+
+public class TodoListExtensionTest {
+
+    @Test
+    public void testGetTaskByUniqueId() {
+
+        TodoListExtension todoList = new TodoListExtension();
+
+        TodoListExtension.TaskExt task1 = new TodoListExtension.TaskExt("running", 5);
+        TodoListExtension.TaskExt task2 = new TodoListExtension.TaskExt("shopping", 3);
+
+        todoList.addTaskExt(task1.task, task1.id);
+        todoList.addTaskExt(task2.task, task2.id);
+
+        Assertions.assertEquals("running", todoList.getTaskByUniqueId(5).task);
+        Assertions.assertEquals("shopping", todoList.getTaskByUniqueId(3).task);
+    }
+
+    @Test
+    public void testUpdateNameBasedOnId() {
+
+        TodoListExtension todoList = new TodoListExtension();
+
+        TodoListExtension.TaskExt task1 = new TodoListExtension.TaskExt("running", 5);
+        TodoListExtension.TaskExt task2 = new TodoListExtension.TaskExt("shopping", 3);
+
+        todoList.addTaskExt(task1.task, task1.id);
+        todoList.addTaskExt(task2.task, task2.id);
+
+        String newName = "work";
+
+        Assertions.assertEquals(newName, todoList.updateNameBasedOnId(5, newName).task);
+    }
+
+
+    @Test
+    public void testUpdateStatusBasedOnId() {
+
+        TodoListExtension todoList = new TodoListExtension();
+
+        TodoListExtension.TaskExt task1 = new TodoListExtension.TaskExt("running", 5);
+        TodoListExtension.TaskExt task2 = new TodoListExtension.TaskExt("shopping", 3);
+
+        todoList.addTaskExt(task1.task, task1.id);
+        todoList.addTaskExt(task2.task, task2.id);
+
+        String newStatus = "complete";
+
+        Assertions.assertEquals(newStatus, todoList.updateStatusBasedOnId(5, newStatus).status);
+    }
+
+
+    @Test
+    public void testWhenTaskCreated() {
+
+        TodoListExtension todoList = new TodoListExtension();
+
+        TodoListExtension.TaskExt task1 = new TodoListExtension.TaskExt("running", 5);
+        TodoListExtension.TaskExt task2 = new TodoListExtension.TaskExt("shopping", 3);
+
+        int currentDateTime = LocalDateTime.now().getHour();
+        todoList.addTaskExt(task1.task, task1.id);
+        todoList.addTaskExt(task2.task, task2.id);
+
+        Assertions.assertEquals(currentDateTime, todoList.whenTaskCreated(5).getHour());
+    }
+}
+