diff --git a/internal/handlers/app.go b/internal/handlers/app.go
index 5c634ca..46d957e 100644
--- a/internal/handlers/app.go
+++ b/internal/handlers/app.go
@@ -41,7 +41,7 @@ func (h *Handlers) HandleAppNew() http.HandlerFunc {
 }
 
 // HandleAppCreate handles app creation.
-func (h *Handlers) HandleAppCreate() http.HandlerFunc {
+func (h *Handlers) HandleAppCreate() http.HandlerFunc { //nolint:funlen // validation adds necessary length
 	tmpl := templates.GetParsed()
 
 	return func(writer http.ResponseWriter, request *http.Request) {
@@ -71,6 +71,14 @@ func (h *Handlers) HandleAppCreate() http.HandlerFunc {
 			return
 		}
 
+		nameErr := validateAppName(name)
+		if nameErr != nil {
+			data["Error"] = "Invalid app name: " + nameErr.Error()
+			_ = tmpl.ExecuteTemplate(writer, "app_new.html", data)
+
+			return
+		}
+
 		if branch == "" {
 			branch = "main"
 		}
@@ -194,7 +202,7 @@ func (h *Handlers) HandleAppEdit() http.HandlerFunc {
 }
 
 // HandleAppUpdate handles app updates.
-func (h *Handlers) HandleAppUpdate() http.HandlerFunc {
+func (h *Handlers) HandleAppUpdate() http.HandlerFunc { //nolint:funlen // validation adds necessary length
 	tmpl := templates.GetParsed()
 
 	return func(writer http.ResponseWriter, request *http.Request) {
@@ -214,7 +222,20 @@ func (h *Handlers) HandleAppUpdate() http.HandlerFunc {
 			return
 		}
 
-		application.Name = request.FormValue("name")
+		newName := request.FormValue("name")
+
+		nameErr := validateAppName(newName)
+		if nameErr != nil {
+			data := h.addGlobals(map[string]any{
+				"App":   application,
+				"Error": "Invalid app name: " + nameErr.Error(),
+			}, request)
+			_ = tmpl.ExecuteTemplate(writer, "app_edit.html", data)
+
+			return
+		}
+
+		application.Name = newName
 		application.RepoURL = request.FormValue("repo_url")
 		application.Branch = request.FormValue("branch")
 		application.DockerfilePath = request.FormValue("dockerfile_path")
diff --git a/internal/handlers/app_name_validation.go b/internal/handlers/app_name_validation.go
new file mode 100644
index 0000000..d1d1abb
--- /dev/null
+++ b/internal/handlers/app_name_validation.go
@@ -0,0 +1,44 @@
+package handlers
+
+import (
+	"errors"
+	"regexp"
+	"strconv"
+)
+
+const (
+	// appNameMinLength is the minimum allowed length for an app name.
+	appNameMinLength = 2
+	// appNameMaxLength is the maximum allowed length for an app name.
+	appNameMaxLength = 63
+)
+
+// validAppNameRe matches names containing only lowercase alphanumeric characters and
+// hyphens, starting and ending with an alphanumeric character.
+var validAppNameRe = regexp.MustCompile(`^[a-z0-9][a-z0-9-]*[a-z0-9]$`)
+
+// validateAppName checks that the given app name is safe for use in Docker
+// container names, image tags, and file system paths.
+var (
+	errAppNameLength = errors.New(
+		"app name must be between " +
+			strconv.Itoa(appNameMinLength) + " and " +
+			strconv.Itoa(appNameMaxLength) + " characters",
+	)
+	errAppNamePattern = errors.New(
+		"app name must contain only lowercase letters, numbers, " +
+			"and hyphens, and must start and end with a letter or number",
+	)
+)
+
+func validateAppName(name string) error {
+	if len(name) < appNameMinLength || len(name) > appNameMaxLength {
+		return errAppNameLength
+	}
+
+	if !validAppNameRe.MatchString(name) {
+		return errAppNamePattern
+	}
+
+	return nil
+}
diff --git a/internal/handlers/app_name_validation_test.go b/internal/handlers/app_name_validation_test.go
new file mode 100644
index 0000000..2811116
--- /dev/null
+++ b/internal/handlers/app_name_validation_test.go
@@ -0,0 +1,48 @@
+package handlers //nolint:testpackage // testing unexported validateAppName
+
+import (
+	"testing"
+)
+
+func TestValidateAppName(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		input   string
+		wantErr bool
+	}{
+		{"valid simple", "myapp", false},
+		{"valid with hyphen", "my-app", false},
+		{"valid with numbers", "app123", false},
+		{"valid two chars", "ab", false},
+		{"valid complex", "my-cool-app-v2", false},
+		{"valid all numbers", "123", false},
+		{"empty", "", true},
+		{"single char", "a", true},
+		{"too long", "a" + string(make([]byte, 63)), true},
+		{"exactly 63 chars", "a23456789012345678901234567890123456789012345678901234567890123", false},
+		{"64 chars", "a234567890123456789012345678901234567890123456789012345678901234", true},
+		{"uppercase", "MyApp", true},
+		{"spaces", "my app", true},
+		{"starts with hyphen", "-myapp", true},
+		{"ends with hyphen", "myapp-", true},
+		{"underscore", "my_app", true},
+		{"dot", "my.app", true},
+		{"slash", "my/app", true},
+		{"path traversal", "../etc/passwd", true},
+		{"special chars", "app@name!", true},
+		{"unicode", "appñame", true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			err := validateAppName(tt.input)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("validateAppName(%q) error = %v, wantErr %v", tt.input, err, tt.wantErr)
+			}
+		})
+	}
+}