diff --git a/marketplace/builder.go b/marketplace/builder.go
index d0d597c..9e7e6aa 100644
--- a/marketplace/builder.go
+++ b/marketplace/builder.go
@@ -7,6 +7,7 @@ import (
 	json "dappco.re/go/core/scm/internal/ax/jsonx"
 	os "dappco.re/go/core/scm/internal/ax/osx"
 	"sort"
+	"strings"
 
 	core "dappco.re/go/core"
 
@@ -23,7 +24,7 @@ const IndexVersion = 1
 type Builder struct {
 	// BaseURL is the prefix for constructing repository URLs, e.g.
 	// "https://forge.lthn.ai". When set, module Repo is derived as
-	// BaseURL + "/" + org + "/" + code.
+	// BaseURL + "/" + org + "/" + code + ".git".
 	BaseURL string
 
 	// Org is the default organisation used when constructing Repo URLs.
@@ -160,8 +161,13 @@ func (b *Builder) loadFromDir(dir string) (*manifest.Manifest, error) {
 
 // repoURL constructs a module repository URL from the builder config.
 func (b *Builder) repoURL(code string) string {
-	if b.BaseURL == "" || b.Org == "" {
+	if b.Org == "" {
 		return ""
 	}
-	return b.BaseURL + "/" + b.Org + "/" + code
+	baseURL := b.BaseURL
+	if baseURL == "" {
+		baseURL = defaultForgeURL
+	}
+	baseURL = strings.TrimSuffix(baseURL, "/")
+	return baseURL + "/" + b.Org + "/" + code + ".git"
 }
diff --git a/marketplace/builder_test.go b/marketplace/builder_test.go
index 85e3a80..9eeaa35 100644
--- a/marketplace/builder_test.go
+++ b/marketplace/builder_test.go
@@ -61,7 +61,7 @@ func TestBuildFromDirs_Good_ManifestYAML_Good(t *testing.T) {
 	require.Len(t, idx.Modules, 1)
 	assert.Equal(t, "my-widget", idx.Modules[0].Code)
 	assert.Equal(t, "My Widget", idx.Modules[0].Name)
-	assert.Equal(t, "https://forge.lthn.ai/core/my-widget", idx.Modules[0].Repo)
+	assert.Equal(t, "https://forge.lthn.ai/core/my-widget.git", idx.Modules[0].Repo)
 	assert.Equal(t, IndexVersion, idx.Version)
 }
 
@@ -189,6 +189,20 @@ func TestBuildFromDirs_Good_NoRepoURLWithoutConfig_Good(t *testing.T) {
 	assert.Empty(t, idx.Modules[0].Repo)
 }
 
+func TestBuildFromDirs_Good_DefaultForgeURL_Good(t *testing.T) {
+	root := t.TempDir()
+	modDir := filepath.Join(root, "mod")
+	require.NoError(t, os.MkdirAll(modDir, 0755))
+	writeManifestYAML(t, modDir, "mod", "Module", "1.0.0")
+
+	b := &Builder{Org: "core"}
+	idx, err := b.BuildFromDirs(root)
+	require.NoError(t, err)
+
+	require.Len(t, idx.Modules, 1)
+	assert.Equal(t, "https://forge.lthn.ai/core/mod.git", idx.Modules[0].Repo)
+}
+
 func TestBuildFromManifests_Good(t *testing.T) {
 	manifests := []*manifest.Manifest{
 		{Code: "bravo", Name: "Bravo", Sign: "key-bravo"},
@@ -268,7 +282,7 @@ func TestWriteIndex_Good_RoundTrip_Good(t *testing.T) {
 
 	require.Len(t, parsed.Modules, 1)
 	assert.Equal(t, "roundtrip", parsed.Modules[0].Code)
-	assert.Equal(t, "https://forge.lthn.ai/core/roundtrip", parsed.Modules[0].Repo)
+	assert.Equal(t, "https://forge.lthn.ai/core/roundtrip.git", parsed.Modules[0].Repo)
 }
 
 func TestLoadIndex_Good(t *testing.T) {
diff --git a/marketplace/indexer.go b/marketplace/indexer.go
index d6e07cd..1282fed 100644
--- a/marketplace/indexer.go
+++ b/marketplace/indexer.go
@@ -3,12 +3,16 @@
 package marketplace
 
 import (
+	"fmt"
 	"sort"
+	"strings"
 
 	"dappco.re/go/core/io"
 	"dappco.re/go/core/scm/manifest"
 )
 
+const defaultForgeURL = "https://forge.lthn.ai"
+
 // IndexOptions controls how BuildIndex populates marketplace metadata.
 // Usage: IndexOptions{...}
 type IndexOptions struct {
@@ -16,6 +20,7 @@ type IndexOptions struct {
 	Org string
 
 	// ForgeURL is the base URL used when constructing repo URLs.
+	// If empty, the default Forge URL is used.
 	ForgeURL string
 
 	// CategoryFn assigns a category to a module code.
@@ -27,6 +32,10 @@ type IndexOptions struct {
 // Categories are deduplicated and sorted.
 // Usage: BuildIndex(...)
 func BuildIndex(medium io.Medium, repoPaths []string, opts IndexOptions) (*Index, error) {
+	if opts.ForgeURL == "" {
+		opts.ForgeURL = defaultForgeURL
+	}
+
 	idx := &Index{
 		Version: IndexVersion,
 	}
@@ -52,8 +61,9 @@ func BuildIndex(medium io.Medium, repoPaths []string, opts IndexOptions) (*Index
 			Name:    m.Name,
 			SignKey: m.Sign,
 		}
-		if opts.ForgeURL != "" && opts.Org != "" {
-			module.Repo = opts.ForgeURL + "/" + opts.Org + "/" + m.Code
+		if opts.Org != "" {
+			baseURL := strings.TrimSuffix(opts.ForgeURL, "/")
+			module.Repo = fmt.Sprintf("%s/%s/%s.git", baseURL, opts.Org, m.Code)
 		}
 		if opts.CategoryFn != nil {
 			module.Category = opts.CategoryFn(m.Code)
diff --git a/marketplace/indexer_test.go b/marketplace/indexer_test.go
index e967912..cfa1cdd 100644
--- a/marketplace/indexer_test.go
+++ b/marketplace/indexer_test.go
@@ -48,7 +48,7 @@ sign: key-c
 
 	require.Len(t, idx.Modules, 3)
 	assert.Equal(t, "a", idx.Modules[0].Code)
-	assert.Equal(t, "https://forge.example.com/core/a", idx.Modules[0].Repo)
+	assert.Equal(t, "https://forge.example.com/core/a.git", idx.Modules[0].Repo)
 	assert.Equal(t, "tools", idx.Modules[0].Category)
 	assert.Equal(t, "key-a", idx.Modules[0].SignKey)
 	assert.Equal(t, []string{"products", "tools"}, idx.Categories)