diff --git a/cmd/picoclaw/internal/skills/install.go b/cmd/picoclaw/internal/skills/install.go
index 9bd9cfd90..6c9b2d7c1 100644
--- a/cmd/picoclaw/internal/skills/install.go
+++ b/cmd/picoclaw/internal/skills/install.go
@@ -13,7 +13,7 @@ func newInstallCommand() *cobra.Command {
 
 	cmd := &cobra.Command{
 		Use:   "install",
-		Short: "Install skill from configured registry",
+		Short: "Install skill from GitHub or a registry",
 		Example: `
 picoclaw skills install sipeed/picoclaw-skills/weather
 picoclaw skills install --registry clawhub github
diff --git a/cmd/picoclaw/internal/skills/install_test.go b/cmd/picoclaw/internal/skills/install_test.go
index da66f1c80..a8c6ec7ec 100644
--- a/cmd/picoclaw/internal/skills/install_test.go
+++ b/cmd/picoclaw/internal/skills/install_test.go
@@ -13,7 +13,7 @@ func TestNewInstallSubcommand(t *testing.T) {
 	require.NotNil(t, cmd)
 
 	assert.Equal(t, "install", cmd.Use)
-	assert.Equal(t, "Install skill from configured registry", cmd.Short)
+	assert.Equal(t, "Install skill from GitHub or a registry", cmd.Short)
 
 	assert.Nil(t, cmd.Run)
 	assert.NotNil(t, cmd.RunE)
diff --git a/pkg/tools/skills_install.go b/pkg/tools/skills_install.go
index aaeef6761..b7532fac5 100644
--- a/pkg/tools/skills_install.go
+++ b/pkg/tools/skills_install.go
@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"sync"
 	"time"
 
@@ -15,6 +16,8 @@ import (
 	"github.com/sipeed/picoclaw/pkg/utils"
 )
 
+const defaultSkillRegistryName = "github"
+
 // InstallSkillTool allows the LLM agent to install skills from registries.
 // It shares the same RegistryManager that FindSkillsTool uses,
 // so all registries configured in config are available for installation.
@@ -40,7 +43,7 @@ func (t *InstallSkillTool) Name() string {
 }
 
 func (t *InstallSkillTool) Description() string {
-	return "Install a skill from a registry by slug. Downloads and extracts the skill into the workspace. Use find_skills first to discover available skills."
+	return "Install a skill from a registry by slug. Defaults to GitHub when registry is omitted. Downloads and extracts the skill into the workspace. Use find_skills first to discover available skills."
 }
 
 func (t *InstallSkillTool) Parameters() map[string]any {
@@ -57,14 +60,14 @@ func (t *InstallSkillTool) Parameters() map[string]any {
 			},
 			"registry": map[string]any{
 				"type":        "string",
-				"description": "Registry to install from (required, e.g., 'clawhub')",
+				"description": "Registry to install from (optional, defaults to 'github')",
 			},
 			"force": map[string]any{
 				"type":        "boolean",
 				"description": "Force reinstall if skill already exists (default false)",
 			},
 		},
-		"required": []string{"slug", "registry"},
+		"required": []string{"slug"},
 	}
 }
 
@@ -75,9 +78,15 @@ func (t *InstallSkillTool) Execute(ctx context.Context, args map[string]any) *To
 	defer t.mu.Unlock()
 
 	slug, _ := args["slug"].(string)
+	if strings.TrimSpace(slug) == "" {
+		return ErrorResult("identifier is required and must be a non-empty string")
+	}
 
 	// Validate registry
 	registryName, _ := args["registry"].(string)
+	if registryName == "" {
+		registryName = defaultSkillRegistryName
+	}
 	if err := utils.ValidateSkillIdentifier(registryName); err != nil {
 		return ErrorResult(fmt.Sprintf("invalid registry %q: error: %s", registryName, err.Error()))
 	}
diff --git a/pkg/tools/skills_install_test.go b/pkg/tools/skills_install_test.go
index f0fcaea0a..8fb1d1828 100644
--- a/pkg/tools/skills_install_test.go
+++ b/pkg/tools/skills_install_test.go
@@ -150,16 +150,18 @@ func TestInstallSkillToolParameters(t *testing.T) {
 	required, ok := params["required"].([]string)
 	assert.True(t, ok)
 	assert.Contains(t, required, "slug")
-	assert.Contains(t, required, "registry")
+	assert.NotContains(t, required, "registry")
 }
 
 func TestInstallSkillToolMissingRegistry(t *testing.T) {
-	tool := NewInstallSkillTool(skills.NewRegistryManager(), t.TempDir())
+	registryMgr := skills.NewRegistryManager()
+	registryMgr.AddRegistry(&mockGitHubInstallRegistry{})
+	tool := NewInstallSkillTool(registryMgr, t.TempDir())
 	result := tool.Execute(context.Background(), map[string]any{
 		"slug": "some-skill",
 	})
-	assert.True(t, result.IsError)
-	assert.Contains(t, result.ForLLM, "invalid registry")
+	assert.False(t, result.IsError)
+	assert.Contains(t, result.ForLLM, `Successfully installed skill`)
 }
 
 func TestInstallSkillToolAllowsGitHubURLSlug(t *testing.T) {
diff --git a/web/backend/api/skills.go b/web/backend/api/skills.go
index e6e7c0157..b65b10479 100644
--- a/web/backend/api/skills.go
+++ b/web/backend/api/skills.go
@@ -22,6 +22,8 @@ import (
 	"github.com/sipeed/picoclaw/pkg/utils"
 )
 
+const defaultInstallSkillRegistry = "github"
+
 type skillSupportResponse struct {
 	Skills []skillSupportItem `json:"skills"`
 }
@@ -291,6 +293,9 @@ func (h *Handler) handleInstallSkill(w http.ResponseWriter, r *http.Request) {
 	req.Slug = strings.TrimSpace(req.Slug)
 	req.Registry = strings.TrimSpace(req.Registry)
 	req.Version = strings.TrimSpace(req.Version)
+	if req.Registry == "" {
+		req.Registry = defaultInstallSkillRegistry
+	}
 
 	if validateErr := utils.ValidateSkillIdentifier(req.Registry); validateErr != nil {
 		http.Error(
diff --git a/web/backend/api/skills_test.go b/web/backend/api/skills_test.go
index 85ffbf517..40c633fe3 100644
--- a/web/backend/api/skills_test.go
+++ b/web/backend/api/skills_test.go
@@ -15,6 +15,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/assert"
+
 	"github.com/sipeed/picoclaw/pkg/config"
 )
 
@@ -560,7 +562,8 @@ func TestHandleSearchSkills(t *testing.T) {
 		t.Fatalf("WriteFile() error = %v", err)
 	}
 
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	var server *httptest.Server
+	server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path != "/api/v1/search" {
 			http.NotFound(w, r)
 			return
@@ -644,7 +647,8 @@ func TestHandleSearchSkillsPagination(t *testing.T) {
 	workspace := filepath.Join(t.TempDir(), "workspace")
 	cfg.Agents.Defaults.Workspace = workspace
 
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	var server *httptest.Server
+	server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path != "/api/v1/search" {
 			http.NotFound(w, r)
 			return
@@ -739,7 +743,8 @@ func TestHandleSearchSkillsClampsRegistryFanout(t *testing.T) {
 	workspace := filepath.Join(t.TempDir(), "workspace")
 	cfg.Agents.Defaults.Workspace = workspace
 
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	var server *httptest.Server
+	server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.URL.Path != "/api/v1/search" {
 			http.NotFound(w, r)
 			return
@@ -1014,6 +1019,79 @@ func TestHandleInstallSkillForcePreservesExistingSkillOnFailure(t *testing.T) {
 	}
 }
 
+func TestHandleInstallSkillDefaultsRegistryToGitHub(t *testing.T) {
+	configPath, cleanup := setupOAuthTestEnv(t)
+	defer cleanup()
+
+	cfg, loadErr := config.LoadConfig(configPath)
+	if loadErr != nil {
+		t.Fatalf("LoadConfig() error = %v", loadErr)
+	}
+	workspace := filepath.Join(t.TempDir(), "workspace")
+	cfg.Agents.Defaults.Workspace = workspace
+	if saveErr := config.SaveConfig(configPath, cfg); saveErr != nil {
+		t.Fatalf("SaveConfig() error = %v", saveErr)
+	}
+
+	var server *httptest.Server
+	server = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/repos/foo/bar/contents/.agents/skills/pr-review":
+			assert.Equal(t, "ref=main", r.URL.RawQuery)
+			json.NewEncoder(w).Encode([]map[string]any{
+				{
+					"type":         "file",
+					"name":         "SKILL.md",
+					"download_url": server.URL + "/raw/foo/bar/main/.agents/skills/pr-review/SKILL.md",
+				},
+			})
+		case "/raw/foo/bar/main/.agents/skills/pr-review/SKILL.md":
+			_, _ = w.Write([]byte("---\nname: pr-review\ndescription: PR review skill\n---\n# PR Review\n"))
+		default:
+			http.NotFound(w, r)
+		}
+	}))
+	defer server.Close()
+
+	githubRegistry, ok := cfg.Tools.Skills.Registries.Get("github")
+	if !ok {
+		t.Fatalf("github registry missing from default config")
+	}
+	githubRegistry.BaseURL = server.URL
+	cfg.Tools.Skills.Registries.Set("github", githubRegistry)
+	if saveErr := config.SaveConfig(configPath, cfg); saveErr != nil {
+		t.Fatalf("SaveConfig() error = %v", saveErr)
+	}
+
+	h := NewHandler(configPath)
+	mux := http.NewServeMux()
+	h.RegisterRoutes(mux)
+
+	body, err := json.Marshal(installSkillRequest{
+		Slug: "foo/bar/.agents/skills/pr-review",
+	})
+	if err != nil {
+		t.Fatalf("Marshal() error = %v", err)
+	}
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodPost, "/api/skills/install", bytes.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	mux.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d, body=%s", rec.Code, http.StatusOK, rec.Body.String())
+	}
+
+	var resp installSkillResponse
+	if err := json.Unmarshal(rec.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("Unmarshal() error = %v", err)
+	}
+	if resp.Registry != "github" {
+		t.Fatalf("resp.Registry = %q, want github", resp.Registry)
+	}
+}
+
 func TestHandleInstallSkillRollsBackOnOriginMetadataWriteFailure(t *testing.T) {
 	configPath, cleanup := setupOAuthTestEnv(t)
 	defer cleanup()