diff --git a/backend/internal/api/chats_test.go b/backend/internal/api/chats_test.go
new file mode 100644
index 0000000..49f8796
--- /dev/null
+++ b/backend/internal/api/chats_test.go
@@ -0,0 +1,277 @@
+package api
+
+import (
+	"bytes"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"vessel-backend/internal/database"
+	"vessel-backend/internal/models"
+
+	"github.com/gin-gonic/gin"
+	_ "modernc.org/sqlite"
+)
+
+func setupTestDB(t *testing.T) *sql.DB {
+	db, err := sql.Open("sqlite", ":memory:")
+	if err != nil {
+		t.Fatalf("failed to open test db: %v", err)
+	}
+
+	if err := database.RunMigrations(db); err != nil {
+		t.Fatalf("failed to run migrations: %v", err)
+	}
+
+	return db
+}
+
+func setupRouter(db *sql.DB) *gin.Engine {
+	gin.SetMode(gin.TestMode)
+	r := gin.New()
+	r.Use(gin.Recovery())
+
+	r.GET("/chats", ListChatsHandler(db))
+	r.GET("/chats/grouped", ListGroupedChatsHandler(db))
+	r.GET("/chats/:id", GetChatHandler(db))
+	r.POST("/chats", CreateChatHandler(db))
+	r.PATCH("/chats/:id", UpdateChatHandler(db))
+	r.DELETE("/chats/:id", DeleteChatHandler(db))
+	r.POST("/chats/:id/messages", CreateMessageHandler(db))
+
+	return r
+}
+
+func TestListChatsHandler(t *testing.T) {
+	db := setupTestDB(t)
+	defer db.Close()
+	router := setupRouter(db)
+
+	// Seed some data
+	chat1 := &models.Chat{ID: "chat1", Title: "Chat 1", Model: "gpt-4", Archived: false}
+	chat2 := &models.Chat{ID: "chat2", Title: "Chat 2", Model: "gpt-4", Archived: true}
+	models.CreateChat(db, chat1)
+	models.CreateChat(db, chat2)
+
+	t.Run("List non-archived chats", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("GET", "/chats", nil)
+		router.ServeHTTP(w, req)
+
+		if w.Code != http.StatusOK {
+			t.Errorf("expected status 200, got %d", w.Code)
+		}
+
+		var response map[string][]models.Chat
+		json.Unmarshal(w.Body.Bytes(), &response)
+		if len(response["chats"]) != 1 {
+			t.Errorf("expected 1 chat, got %d", len(response["chats"]))
+		}
+	})
+
+	t.Run("List including archived chats", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("GET", "/chats?include_archived=true", nil)
+		router.ServeHTTP(w, req)
+
+		if w.Code != http.StatusOK {
+			t.Errorf("expected status 200, got %d", w.Code)
+		}
+
+		var response map[string][]models.Chat
+		json.Unmarshal(w.Body.Bytes(), &response)
+		if len(response["chats"]) != 2 {
+			t.Errorf("expected 2 chats, got %d", len(response["chats"]))
+		}
+	})
+}
+
+func TestListGroupedChatsHandler(t *testing.T) {
+	db := setupTestDB(t)
+	defer db.Close()
+	router := setupRouter(db)
+
+	// Seed some data
+	models.CreateChat(db, &models.Chat{ID: "chat1", Title: "Apple Chat", Model: "gpt-4"})
+	models.CreateChat(db, &models.Chat{ID: "chat2", Title: "Banana Chat", Model: "gpt-4"})
+
+	t.Run("Search chats", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("GET", "/chats/grouped?search=Apple", nil)
+		router.ServeHTTP(w, req)
+
+		var resp models.GroupedChatsResponse
+		json.Unmarshal(w.Body.Bytes(), &resp)
+		if resp.Total != 1 {
+			t.Errorf("expected 1 chat, got %d", resp.Total)
+		}
+	})
+
+	t.Run("Pagination", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("GET", "/chats/grouped?limit=1&offset=0", nil)
+		router.ServeHTTP(w, req)
+
+		var resp models.GroupedChatsResponse
+		json.Unmarshal(w.Body.Bytes(), &resp)
+		if len(resp.Groups) != 1 || len(resp.Groups[0].Chats) != 1 {
+			t.Errorf("expected 1 chat in response, got %d", len(resp.Groups[0].Chats))
+		}
+	})
+}
+
+func TestGetChatHandler(t *testing.T) {
+	db := setupTestDB(t)
+	defer db.Close()
+	router := setupRouter(db)
+
+	chat := &models.Chat{ID: "test-chat", Title: "Test Chat", Model: "gpt-4"}
+	models.CreateChat(db, chat)
+
+	t.Run("Get existing chat", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("GET", "/chats/test-chat", nil)
+		router.ServeHTTP(w, req)
+
+		if w.Code != http.StatusOK {
+			t.Errorf("expected status 200, got %d", w.Code)
+		}
+	})
+
+	t.Run("Get non-existent chat", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("GET", "/chats/invalid", nil)
+		router.ServeHTTP(w, req)
+
+		if w.Code != http.StatusNotFound {
+			t.Errorf("expected status 404, got %d", w.Code)
+		}
+	})
+}
+
+func TestCreateChatHandler(t *testing.T) {
+	db := setupTestDB(t)
+	defer db.Close()
+	router := setupRouter(db)
+
+	body := CreateChatRequest{Title: "New Chat Title", Model: "gpt-4"}
+	jsonBody, _ := json.Marshal(body)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("POST", "/chats", bytes.NewBuffer(jsonBody))
+	req.Header.Set("Content-Type", "application/json")
+	router.ServeHTTP(w, req)
+
+	if w.Code != http.StatusCreated {
+		t.Errorf("expected status 201, got %d", w.Code)
+	}
+
+	var chat models.Chat
+	json.Unmarshal(w.Body.Bytes(), &chat)
+	if chat.Title != "New Chat Title" {
+		t.Errorf("expected title 'New Chat Title', got '%s'", chat.Title)
+	}
+}
+
+func TestUpdateChatHandler(t *testing.T) {
+	db := setupTestDB(t)
+	defer db.Close()
+	router := setupRouter(db)
+
+	chat := &models.Chat{ID: "test-chat", Title: "Old Title", Model: "gpt-4"}
+	models.CreateChat(db, chat)
+
+	newTitle := "Updated Title"
+	body := UpdateChatRequest{Title: &newTitle}
+	jsonBody, _ := json.Marshal(body)
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("PATCH", "/chats/test-chat", bytes.NewBuffer(jsonBody))
+	req.Header.Set("Content-Type", "application/json")
+	router.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected status 200, got %d", w.Code)
+	}
+
+	var updatedChat models.Chat
+	json.Unmarshal(w.Body.Bytes(), &updatedChat)
+	if updatedChat.Title != "Updated Title" {
+		t.Errorf("expected title 'Updated Title', got '%s'", updatedChat.Title)
+	}
+}
+
+func TestDeleteChatHandler(t *testing.T) {
+	db := setupTestDB(t)
+	defer db.Close()
+	router := setupRouter(db)
+
+	chat := &models.Chat{ID: "test-chat", Title: "To Delete", Model: "gpt-4"}
+	models.CreateChat(db, chat)
+
+	t.Run("Delete existing chat", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("DELETE", "/chats/test-chat", nil)
+		router.ServeHTTP(w, req)
+
+		if w.Code != http.StatusOK {
+			t.Errorf("expected status 200, got %d", w.Code)
+		}
+	})
+
+	t.Run("Delete non-existent chat", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("DELETE", "/chats/invalid", nil)
+		router.ServeHTTP(w, req)
+
+		if w.Code != http.StatusNotFound {
+			t.Errorf("expected status 404, got %d", w.Code)
+		}
+	})
+}
+
+func TestCreateMessageHandler(t *testing.T) {
+	db := setupTestDB(t)
+	defer db.Close()
+	router := setupRouter(db)
+
+	chat := &models.Chat{ID: "test-chat", Title: "Message Test", Model: "gpt-4"}
+	models.CreateChat(db, chat)
+
+	t.Run("Create valid message", func(t *testing.T) {
+		body := CreateMessageRequest{
+			Role:    "user",
+			Content: "Hello world",
+		}
+		jsonBody, _ := json.Marshal(body)
+
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("POST", "/chats/test-chat/messages", bytes.NewBuffer(jsonBody))
+		req.Header.Set("Content-Type", "application/json")
+		router.ServeHTTP(w, req)
+
+		if w.Code != http.StatusCreated {
+			t.Errorf("expected status 201, got %d", w.Code)
+			fmt.Println(w.Body.String())
+		}
+	})
+
+	t.Run("Create message with invalid role", func(t *testing.T) {
+		body := CreateMessageRequest{
+			Role:    "invalid",
+			Content: "Hello world",
+		}
+		jsonBody, _ := json.Marshal(body)
+
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("POST", "/chats/test-chat/messages", bytes.NewBuffer(jsonBody))
+		req.Header.Set("Content-Type", "application/json")
+		router.ServeHTTP(w, req)
+
+		if w.Code != http.StatusBadRequest {
+			t.Errorf("expected status 400, got %d", w.Code)
+		}
+	})
+}