diff --git a/server/api/habits/[id]/complete.post.ts b/server/api/habits/[id]/complete.post.ts
new file mode 100644
index 0000000..36b25f3
--- /dev/null
+++ b/server/api/habits/[id]/complete.post.ts
@@ -0,0 +1,87 @@
+import { useSession } from 'h3';
+
+interface CompletionResponse {
+  message: string;
+  reward: {
+    coins: number;
+  };
+  updatedCoins: number;
+}
+
+/**
+ * A helper function to safely get the authenticated user's ID from the session.
+ */
+async function getUserIdFromSession(event: any): Promise<number> {
+  const session = await useSession(event, {
+    password: process.env.SESSION_PASSWORD,
+  });
+  const userId = session.data?.user?.id;
+  if (!userId) {
+    throw createError({ statusCode: 401, statusMessage: 'Unauthorized' });
+  }
+  return userId;
+}
+
+export default defineEventHandler(async (event): Promise<CompletionResponse> => {
+  const userId = await getUserIdFromSession(event);
+  const habitId = parseInt(event.context.params?.id || '', 10);
+
+  if (isNaN(habitId)) {
+    throw createError({ statusCode: 400, statusMessage: 'Invalid habit ID.' });
+  }
+
+  const habit = await prisma.habit.findFirst({
+    where: { id: habitId, userId },
+  });
+
+  if (!habit) {
+    throw createError({ statusCode: 404, statusMessage: 'Habit not found.' });
+  }
+
+  const today = new Date();
+  const dayOfWeek = today.getDay(); // 0 (Sunday) to 6 (Saturday)
+  if (!(habit.daysOfWeek as number[]).includes(dayOfWeek)) {
+    throw createError({ statusCode: 400, statusMessage: 'Habit is not active today.' });
+  }
+
+  // Normalize date to the beginning of the day for consistent checks
+  const startOfToday = new Date();
+  startOfToday.setUTCHours(0, 0, 0, 0);
+
+  const existingCompletion = await prisma.habitCompletion.findFirst({
+    where: {
+      habitId: habitId,
+      date: startOfToday, // Use precise equality check
+    },
+  });
+
+  if (existingCompletion) {
+    throw createError({ statusCode: 409, statusMessage: 'Habit already completed today.' });
+  }
+
+  const rewardCoins = 3;
+  const [, updatedUser] = await prisma.$transaction([
+    prisma.habitCompletion.create({
+      data: {
+        habitId: habitId,
+        date: startOfToday, // Save the normalized date
+      },
+    }),
+    prisma.user.update({
+      where: { id: userId },
+      data: {
+        coins: {
+          increment: rewardCoins,
+        },
+      },
+    }),
+  ]);
+
+  return {
+    message: 'Habit completed successfully!',
+    reward: {
+      coins: rewardCoins,
+    },
+    updatedCoins: updatedUser.coins,
+  };
+});
diff --git a/server/api/habits/index.get.ts b/server/api/habits/index.get.ts
new file mode 100644
index 0000000..11c341a
--- /dev/null
+++ b/server/api/habits/index.get.ts
@@ -0,0 +1,56 @@
+import { useSession } from 'h3';
+
+// DTO to shape the output
+interface HabitCompletionDto {
+  date: Date;
+}
+
+interface HabitDto {
+  id: number;
+  name: string;
+  daysOfWeek: number[];
+  completions: HabitCompletionDto[];
+}
+
+/**
+ * A helper function to safely get the authenticated user's ID from the session.
+ */
+async function getUserIdFromSession(event: any): Promise<number> {
+  const session = await useSession(event, {
+    password: process.env.SESSION_PASSWORD,
+  });
+
+  const userId = session.data?.user?.id;
+  if (!userId) {
+    throw createError({ statusCode: 401, statusMessage: 'Unauthorized' });
+  }
+  return userId;
+}
+
+export default defineEventHandler(async (event): Promise<HabitDto[]> => {
+  const userId = await getUserIdFromSession(event);
+
+  const habits = await prisma.habit.findMany({
+    where: {
+      userId: userId,
+    },
+    include: {
+      completions: {
+        orderBy: {
+          date: 'desc',
+        },
+        take: 30, // Limit completions to the last 30 for performance
+      },
+    },
+  });
+
+  // Map to DTOs
+  return habits.map((habit: any) => ({
+    id: habit.id,
+    name: habit.name,
+    daysOfWeek: habit.daysOfWeek, // Assuming daysOfWeek is already in the correct format
+    completions: habit.completions.map((comp: any) => ({
+      date: comp.date,
+    })),
+  }));
+});
diff --git a/server/api/habits/index.post.ts b/server/api/habits/index.post.ts
new file mode 100644
index 0000000..701e874
--- /dev/null
+++ b/server/api/habits/index.post.ts
@@ -0,0 +1,62 @@
+import { useSession } from 'h3';
+
+interface HabitDto {
+  id: number;
+  name: string;
+  daysOfWeek: number[];
+}
+
+/**
+ * A helper function to safely get the authenticated user's ID from the session.
+ */
+async function getUserIdFromSession(event: any): Promise<number> {
+  const session = await useSession(event, {
+    password: process.env.SESSION_PASSWORD,
+  });
+
+  const userId = session.data?.user?.id;
+  if (!userId) {
+    throw createError({ statusCode: 401, statusMessage: 'Unauthorized' });
+  }
+  return userId;
+}
+
+export default defineEventHandler(async (event): Promise<HabitDto> => {
+  const userId = await getUserIdFromSession(event);
+  const { name, daysOfWeek } = await readBody(event);
+
+  // --- Validation ---
+  if (!name || !Array.isArray(daysOfWeek)) {
+    throw createError({ statusCode: 400, statusMessage: 'Invalid input: name and daysOfWeek are required.' });
+  }
+
+  // Sanitize daysOfWeek to ensure it's a unique set of valid numbers
+  const validDays = daysOfWeek.filter(day => typeof day === 'number' && day >= 0 && day <= 6);
+  const sanitizedDays = [...new Set(validDays)].sort();
+
+
+  // --- Business Rule: Max 3 Habits ---
+  const habitCount = await prisma.habit.count({ where: { userId } });
+  if (habitCount >= 3) {
+    throw createError({ statusCode: 400, statusMessage: 'Maximum number of 3 habits reached.' });
+  }
+
+  // --- Create Habit ---
+  const newHabit = await prisma.habit.create({
+    data: {
+      userId,
+      name,
+      daysOfWeek: sanitizedDays,
+    },
+  });
+
+  // Set 201 Created status
+  setResponseStatus(event, 201);
+  
+  // Return DTO
+  return {
+    id: newHabit.id,
+    name: newHabit.name,
+    daysOfWeek: newHabit.daysOfWeek as number[],
+  };
+});