diff --git a/internal/route/route.go b/internal/route/route.go
index 04a14fed..27897ed0 100644
--- a/internal/route/route.go
+++ b/internal/route/route.go
@@ -55,7 +55,7 @@ type (
 
 		route.HTTPConfig
 		PathPatterns []string                       `json:"path_patterns,omitempty" extensions:"x-nullable"`
-		Rules        rules.Rules                    `json:"rules,omitempty" extension:"x-nullable"`
+		Rules        rules.Rules                    `json:"rules,omitempty" extensions:"x-nullable"`
 		RuleFile     string                         `json:"rule_file,omitempty" extensions:"x-nullable"`
 		HealthCheck  types.HealthCheckConfig        `json:"healthcheck,omitempty" extensions:"x-nullable"` // null on load-balancer routes
 		LoadBalance  *types.LoadBalancerConfig      `json:"load_balance,omitempty" extensions:"x-nullable"`
diff --git a/internal/route/rules/errors.go b/internal/route/rules/errors.go
index f99a7091..4d310559 100644
--- a/internal/route/rules/errors.go
+++ b/internal/route/rules/errors.go
@@ -15,6 +15,7 @@ var (
 	ErrInvalidArguments        = gperr.New("invalid arguments")
 	ErrInvalidOnTarget         = gperr.New("invalid `rule.on` target")
 	ErrInvalidCommandSequence  = gperr.New("invalid command sequence")
+	ErrMultipleDefaultRules    = gperr.New("multiple default rules")
 
 	// vars errors
 	ErrNoArgProvided   = gperr.New("no argument provided")
diff --git a/internal/route/rules/on.go b/internal/route/rules/on.go
index 6d017b0f..4471c656 100644
--- a/internal/route/rules/on.go
+++ b/internal/route/rules/on.go
@@ -26,6 +26,7 @@ func (on *RuleOn) Check(w http.ResponseWriter, r *http.Request) bool {
 }
 
 const (
+	OnDefault   = "default"
 	OnHeader    = "header"
 	OnQuery     = "query"
 	OnCookie    = "cookie"
@@ -50,6 +51,22 @@ var checkers = map[string]struct {
 	builder           func(args any) CheckFunc
 	isResponseChecker bool
 }{
+	OnDefault: {
+		help: Help{
+			command: OnDefault,
+			description: makeLines(
+				"The default rule is matched when no other rules are matched.",
+			),
+			args: map[string]string{},
+		},
+		validate: func(args []string) (any, gperr.Error) {
+			if len(args) != 0 {
+				return nil, ErrExpectNoArg
+			}
+			return nil, nil
+		},
+		builder: func(args any) CheckFunc { return func(w http.ResponseWriter, r *http.Request) bool { return false } }, // this should never be called
+	},
 	OnHeader: {
 		help: Help{
 			command: OnHeader,
diff --git a/internal/route/rules/rules.go b/internal/route/rules/rules.go
index ab014492..0fbf9b88 100644
--- a/internal/route/rules/rules.go
+++ b/internal/route/rules/rules.go
@@ -7,6 +7,7 @@ import (
 
 	"github.com/quic-go/quic-go/http3"
 	"github.com/rs/zerolog/log"
+	gperr "github.com/yusing/goutils/errs"
 	httputils "github.com/yusing/goutils/http"
 	"golang.org/x/net/http2"
 
@@ -57,6 +58,19 @@ func (rule *Rule) IsResponseRule() bool {
 	return rule.On.IsResponseChecker() || rule.Do.IsResponseHandler()
 }
 
+func (rules Rules) Validate() gperr.Error {
+	var defaultRulesFound []int
+	for i, rule := range rules {
+		if rule.Name == "default" || rule.On.raw == OnDefault {
+			defaultRulesFound = append(defaultRulesFound, i)
+		}
+	}
+	if len(defaultRulesFound) > 1 {
+		return ErrMultipleDefaultRules.Withf("found %d", len(defaultRulesFound))
+	}
+	return nil
+}
+
 // BuildHandler returns a http.HandlerFunc that implements the rules.
 func (rules Rules) BuildHandler(up http.HandlerFunc) http.HandlerFunc {
 	if len(rules) == 0 {
@@ -74,7 +88,7 @@ func (rules Rules) BuildHandler(up http.HandlerFunc) http.HandlerFunc {
 	var nonDefaultRules Rules
 	hasDefaultRule := false
 	for i, rule := range rules {
-		if rule.Name == "default" {
+		if rule.Name == "default" || rule.On.raw == OnDefault {
 			defaultRule = rule
 			hasDefaultRule = true
 		} else {
diff --git a/internal/route/rules/rules_test.go b/internal/route/rules/rules_test.go
new file mode 100644
index 00000000..7a4b2e81
--- /dev/null
+++ b/internal/route/rules/rules_test.go
@@ -0,0 +1,52 @@
+package rules
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/yusing/godoxy/internal/serialization"
+)
+
+func TestRulesValidate(t *testing.T) {
+	tests := []struct {
+		name  string
+		rules string
+		want  error
+	}{
+		{
+			name: "no default rule",
+			rules: `
+- name: rule1
+  on: header Host example.com
+  do: pass
+      `,
+		},
+		{
+			name: "multiple default rules",
+			rules: `
+- name: default
+  do: pass
+- name: rule1
+  on: default
+  do: pass
+      `,
+			want: ErrMultipleDefaultRules,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var rules Rules
+			convertible, err := serialization.ConvertString(strings.TrimSpace(tt.rules), reflect.ValueOf(&rules))
+			require.True(t, convertible)
+
+			if tt.want == nil {
+				assert.NoError(t, err)
+				return
+			}
+			assert.ErrorIs(t, err, tt.want)
+		})
+	}
+}