diff --git a/internal/commands/exit_codes.go b/internal/commands/exit_codes.go
index c2b1d58..d7afea3 100644
--- a/internal/commands/exit_codes.go
+++ b/internal/commands/exit_codes.go
@@ -36,4 +36,10 @@ const (
 	// ExitConfigError indicates a configuration error
 	// (missing config file, invalid YAML, no server configured)
 	ExitConfigError = 8
+
+	// ExitDiffChanges indicates `sc theme diff --exit-code` found differences
+	// between the local theme and the server. It is NOT an error — the command
+	// succeeded; this code lets CI distinguish "theme has undeployed drift"
+	// from a genuine failure (which uses ExitGenericError and friends).
+	ExitDiffChanges = 9
 )
diff --git a/internal/commands/responses.go b/internal/commands/responses.go
index 03720fc..d5517c0 100644
--- a/internal/commands/responses.go
+++ b/internal/commands/responses.go
@@ -1,6 +1,10 @@
 package commands
 
-import "time"
+import (
+	"time"
+
+	"github.com/GetStoreConnect/storeconnect-cli/internal/theme"
+)
 
 // SuccessResponse is the standard JSON success response format
 type SuccessResponse struct {
@@ -83,3 +87,14 @@ type ThemePublishResponse struct {
 	Status          string `json:"status"`
 	Message         string `json:"message,omitempty"`
 }
+
+// ThemeDiffResponse is the response for the theme diff command: the divergence
+// between the local theme and the server, plus rolled-up counts.
+type ThemeDiffResponse struct {
+	ThemeName  string             `json:"theme_name"`
+	Templates  theme.CategoryDiff `json:"templates"`
+	Assets     theme.CategoryDiff `json:"assets"`
+	HasChanges bool               `json:"has_changes"`
+	Pushable   int                `json:"pushable"`
+	ServerOnly int                `json:"server_only"`
+}
diff --git a/internal/commands/theme_diff.go b/internal/commands/theme_diff.go
new file mode 100644
index 0000000..ae4899e
--- /dev/null
+++ b/internal/commands/theme_diff.go
@@ -0,0 +1,162 @@
+package commands
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/GetStoreConnect/storeconnect-cli/internal/api"
+	"github.com/GetStoreConnect/storeconnect-cli/internal/config"
+	"github.com/GetStoreConnect/storeconnect-cli/internal/theme"
+	"github.com/GetStoreConnect/storeconnect-cli/internal/ui"
+	"github.com/fatih/color"
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	themeCmd.AddCommand(themeDiffCmd)
+	themeDiffCmd.Flags().Bool("exit-code", false, "exit with code 9 when the local theme differs from the server (for CI)")
+}
+
+var themeDiffCmd = &cobra.Command{
+	Use:   "diff THEME_NAME",
+	Short: "Show how the local theme differs from the server",
+	Long: `Compare a local theme against the server's copy without pushing.
+
+Shows which templates and asset binaries have been added, modified, or only
+exist on the server. This is the read-only sibling of 'sc theme push' — it
+reports exactly what a push would send.
+
+With --exit-code the command exits 9 when there are any differences, so CI can
+gate on a theme being in sync with what's deployed:
+
+    sc theme diff my-theme --exit-code || echo "theme has undeployed changes"`,
+	Args: cobra.ExactArgs(1),
+	RunE: runThemeDiff,
+}
+
+func runThemeDiff(cmd *cobra.Command, args []string) error {
+	themeName := args[0]
+	formatter := ui.NewFormatter()
+	exitCode, _ := cmd.Flags().GetBool("exit-code")
+
+	client, serverAlias, err := getAPIClient(cmd)
+	if err != nil {
+		if !jsonOutput {
+			formatter.Error(fmt.Sprintf("Failed to get API client: %v", err))
+		}
+		return outputError(err)
+	}
+
+	var spinner *ui.Spinner
+	if !jsonOutput {
+		spinner = ui.NewSpinner(fmt.Sprintf("Comparing theme '%s'", themeName))
+		spinner.Start()
+	}
+
+	// Read the local theme (templates) and its asset binaries.
+	deserializer := theme.NewDeserializer(".")
+	localTheme, err := deserializer.Deserialize(themeName)
+	if err != nil {
+		if spinner != nil {
+			spinner.Error(fmt.Sprintf("Failed to read theme: %v", err))
+		}
+		return outputError(err)
+	}
+
+	themeDir := fmt.Sprintf("themes/%s", themeName)
+	localAssets, err := theme.ReadLocalAssets(themeDir)
+	if err != nil {
+		if spinner != nil {
+			spinner.Error(fmt.Sprintf("Failed to read assets: %v", err))
+		}
+		return outputError(err)
+	}
+
+	// Resolve the server-side theme id the same way push does.
+	themeID := localTheme.SCID
+	if themeID == "" {
+		if syncState, sErr := config.NewSyncState(themeDir); sErr == nil {
+			themeID = syncState.ThemeSCID
+		}
+	}
+	if themeID == "" {
+		if spinner != nil {
+			spinner.Error("Theme has no SC ID. Pull the theme first or create it on the server.")
+		}
+		return fmt.Errorf("theme has no sc_id")
+	}
+
+	themesService := api.NewThemes(client)
+	serverTheme, err := themesService.Get(themeID)
+	if err != nil {
+		if spinner != nil {
+			spinner.Error(fmt.Sprintf("Failed to fetch server theme: %v", err))
+		}
+		return outputError(err)
+	}
+
+	if spinner != nil {
+		spinner.Stop()
+	}
+
+	diff := theme.ComputeDiff(localTheme, localAssets, serverTheme)
+
+	if jsonOutput {
+		if err := outputResponse(ThemeDiffResponse{
+			ThemeName:  themeName,
+			Templates:  diff.Templates,
+			Assets:     diff.Assets,
+			HasChanges: diff.HasChanges(),
+			Pushable:   diff.PushableCount(),
+			ServerOnly: diff.ServerOnlyCount(),
+		}, nil); err != nil {
+			return err
+		}
+	} else {
+		renderDiff(formatter, themeName, serverAlias, diff)
+	}
+
+	if exitCode && diff.HasChanges() {
+		os.Exit(ExitDiffChanges)
+	}
+
+	return nil
+}
+
+func renderDiff(formatter *ui.Formatter, themeName, serverAlias string, diff theme.Diff) {
+	if !diff.HasChanges() {
+		formatter.Success(fmt.Sprintf("Theme '%s' is in sync with %s", themeName, serverAlias))
+		return
+	}
+
+	formatter.Info(fmt.Sprintf("Diff for theme '%s' against %s:", themeName, serverAlias))
+
+	renderCategory(formatter, "Templates", diff.Templates)
+	renderCategory(formatter, "Assets", diff.Assets)
+
+	formatter.Newline()
+	formatter.Dim(fmt.Sprintf("%d to push, %d only on server", diff.PushableCount(), diff.ServerOnlyCount()))
+}
+
+func renderCategory(formatter *ui.Formatter, label string, c theme.CategoryDiff) {
+	if len(c.Added)+len(c.Modified)+len(c.Removed) == 0 {
+		return
+	}
+
+	formatter.Newline()
+	formatter.Print(label + ":")
+
+	added := color.New(color.FgGreen).SprintFunc()
+	modified := color.New(color.FgYellow).SprintFunc()
+	removed := color.New(color.FgRed).SprintFunc()
+
+	for _, key := range c.Added {
+		fmt.Printf("  %s %s\n", added("+"), key)
+	}
+	for _, key := range c.Modified {
+		fmt.Printf("  %s %s\n", modified("~"), key)
+	}
+	for _, key := range c.Removed {
+		fmt.Printf("  %s %s\n", removed("-"), key)
+	}
+}
diff --git a/internal/theme/diff.go b/internal/theme/diff.go
new file mode 100644
index 0000000..e92e5e1
--- /dev/null
+++ b/internal/theme/diff.go
@@ -0,0 +1,126 @@
+package theme
+
+import (
+	"sort"
+
+	"github.com/GetStoreConnect/storeconnect-cli/internal/api"
+)
+
+// CategoryDiff holds the keys that differ between local and server for one
+// category of theme content (templates or assets). Added are present locally
+// but not on the server; Removed are present on the server but not locally;
+// Modified are present in both but with differing content. All slices are
+// sorted for stable output.
+type CategoryDiff struct {
+	Added    []string `json:"added"`
+	Modified []string `json:"modified"`
+	Removed  []string `json:"removed"`
+}
+
+// count returns the total number of differing keys in this category.
+func (c CategoryDiff) count() int {
+	return len(c.Added) + len(c.Modified) + len(c.Removed)
+}
+
+// Diff is the full divergence between a local theme and the server's copy.
+type Diff struct {
+	Templates CategoryDiff `json:"templates"`
+	Assets    CategoryDiff `json:"assets"`
+}
+
+// HasChanges reports whether the local theme differs from the server in any way.
+func (d Diff) HasChanges() bool {
+	return d.Templates.count() > 0 || d.Assets.count() > 0
+}
+
+// PushableCount is the number of keys that `sc theme push` would send: added
+// and modified templates and assets. Removed keys (present on the server but
+// not locally) are excluded because push never deletes server content.
+func (d Diff) PushableCount() int {
+	return len(d.Templates.Added) + len(d.Templates.Modified) +
+		len(d.Assets.Added) + len(d.Assets.Modified)
+}
+
+// ServerOnlyCount is the number of keys present on the server but not locally
+// (removed templates and assets) — divergence that push will not reconcile.
+func (d Diff) ServerOnlyCount() int {
+	return len(d.Templates.Removed) + len(d.Assets.Removed)
+}
+
+// ComputeDiff compares a local theme against the server's copy. Templates are
+// compared by key, treating a content difference as a modification. Assets are
+// compared by key using their SHA-256 content hash, so an unchanged binary is
+// never reported even though its bytes are read locally. ComputeDiff is pure so
+// the comparison rule is trivially unit-testable.
+func ComputeDiff(local *api.Theme, localAssets []LocalAsset, server *api.Theme) Diff {
+	return Diff{
+		Templates: diffTemplates(local, server),
+		Assets:    diffAssets(localAssets, server),
+	}
+}
+
+func diffTemplates(local, server *api.Theme) CategoryDiff {
+	localByKey := make(map[string]string, len(local.Templates))
+	for _, t := range local.Templates {
+		localByKey[t.Key] = t.Content
+	}
+	serverByKey := make(map[string]string, len(server.Templates))
+	for _, t := range server.Templates {
+		serverByKey[t.Key] = t.Content
+	}
+
+	var diff CategoryDiff
+	for key, localContent := range localByKey {
+		serverContent, exists := serverByKey[key]
+		switch {
+		case !exists:
+			diff.Added = append(diff.Added, key)
+		case localContent != serverContent:
+			diff.Modified = append(diff.Modified, key)
+		}
+	}
+	for key := range serverByKey {
+		if _, exists := localByKey[key]; !exists {
+			diff.Removed = append(diff.Removed, key)
+		}
+	}
+
+	sortCategory(&diff)
+	return diff
+}
+
+func diffAssets(local []LocalAsset, server *api.Theme) CategoryDiff {
+	localByKey := make(map[string]string, len(local))
+	for _, a := range local {
+		localByKey[a.Key] = a.ContentHash
+	}
+	serverByKey := make(map[string]string, len(server.Assets))
+	for _, a := range server.Assets {
+		serverByKey[a.Key] = a.ContentHash
+	}
+
+	var diff CategoryDiff
+	for key, localHash := range localByKey {
+		serverHash, exists := serverByKey[key]
+		switch {
+		case !exists:
+			diff.Added = append(diff.Added, key)
+		case localHash != serverHash:
+			diff.Modified = append(diff.Modified, key)
+		}
+	}
+	for key := range serverByKey {
+		if _, exists := localByKey[key]; !exists {
+			diff.Removed = append(diff.Removed, key)
+		}
+	}
+
+	sortCategory(&diff)
+	return diff
+}
+
+func sortCategory(c *CategoryDiff) {
+	sort.Strings(c.Added)
+	sort.Strings(c.Modified)
+	sort.Strings(c.Removed)
+}
diff --git a/internal/theme/diff_test.go b/internal/theme/diff_test.go
new file mode 100644
index 0000000..f0eb0e2
--- /dev/null
+++ b/internal/theme/diff_test.go
@@ -0,0 +1,126 @@
+package theme
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/GetStoreConnect/storeconnect-cli/internal/api"
+)
+
+func tmpl(key, content string) api.ThemeTemplate {
+	return api.ThemeTemplate{Key: key, Content: content}
+}
+
+func TestComputeDiffTemplates(t *testing.T) {
+	local := &api.Theme{Templates: []api.ThemeTemplate{
+		tmpl("layouts/theme", "CHANGED"), // modified
+		tmpl("pages/home", "same"),       // unchanged
+		tmpl("pages/new", "brand new"),   // added
+	}}
+	server := &api.Theme{Templates: []api.ThemeTemplate{
+		tmpl("layouts/theme", "original"),
+		tmpl("pages/home", "same"),
+		tmpl("pages/gone", "old"), // removed
+	}}
+
+	diff := ComputeDiff(local, nil, server)
+
+	if !reflect.DeepEqual(diff.Templates.Added, []string{"pages/new"}) {
+		t.Errorf("added = %v", diff.Templates.Added)
+	}
+	if !reflect.DeepEqual(diff.Templates.Modified, []string{"layouts/theme"}) {
+		t.Errorf("modified = %v", diff.Templates.Modified)
+	}
+	if !reflect.DeepEqual(diff.Templates.Removed, []string{"pages/gone"}) {
+		t.Errorf("removed = %v", diff.Templates.Removed)
+	}
+}
+
+func TestComputeDiffAssets(t *testing.T) {
+	local := []LocalAsset{
+		{Key: "logo.png", ContentHash: "newhash"},      // modified
+		{Key: "fonts/brand.woff2", ContentHash: "abc"}, // added
+		{Key: "icon.svg", ContentHash: "same"},         // unchanged
+	}
+	server := &api.Theme{Assets: []api.ThemeAsset{
+		{Key: "logo.png", ContentHash: "oldhash"},
+		{Key: "icon.svg", ContentHash: "same"},
+		{Key: "legacy.gif", ContentHash: "x"}, // removed
+	}}
+
+	diff := ComputeDiff(&api.Theme{}, local, server)
+
+	if !reflect.DeepEqual(diff.Assets.Added, []string{"fonts/brand.woff2"}) {
+		t.Errorf("added = %v", diff.Assets.Added)
+	}
+	if !reflect.DeepEqual(diff.Assets.Modified, []string{"logo.png"}) {
+		t.Errorf("modified = %v", diff.Assets.Modified)
+	}
+	if !reflect.DeepEqual(diff.Assets.Removed, []string{"legacy.gif"}) {
+		t.Errorf("removed = %v", diff.Assets.Removed)
+	}
+}
+
+func TestComputeDiffInSync(t *testing.T) {
+	local := &api.Theme{Templates: []api.ThemeTemplate{tmpl("layouts/theme", "x")}}
+	localAssets := []LocalAsset{{Key: "logo.png", ContentHash: "h"}}
+	server := &api.Theme{
+		Templates: []api.ThemeTemplate{tmpl("layouts/theme", "x")},
+		Assets:    []api.ThemeAsset{{Key: "logo.png", ContentHash: "h"}},
+	}
+
+	diff := ComputeDiff(local, localAssets, server)
+
+	if diff.HasChanges() {
+		t.Errorf("expected no changes, got %+v", diff)
+	}
+	if diff.PushableCount() != 0 || diff.ServerOnlyCount() != 0 {
+		t.Errorf("expected zero counts, got pushable=%d serverOnly=%d", diff.PushableCount(), diff.ServerOnlyCount())
+	}
+}
+
+func TestComputeDiffCounts(t *testing.T) {
+	local := &api.Theme{Templates: []api.ThemeTemplate{
+		tmpl("a", "1"),       // added
+		tmpl("b", "changed"), // modified
+	}}
+	localAssets := []LocalAsset{{Key: "c.png", ContentHash: "new"}} // added
+	server := &api.Theme{
+		Templates: []api.ThemeTemplate{
+			tmpl("b", "orig"),
+			tmpl("d", "x"), // removed
+		},
+		Assets: []api.ThemeAsset{{Key: "e.png", ContentHash: "y"}}, // removed
+	}
+
+	diff := ComputeDiff(local, localAssets, server)
+
+	if !diff.HasChanges() {
+		t.Fatal("expected changes")
+	}
+	// added a, modified b, added c.png = 3 pushable
+	if diff.PushableCount() != 3 {
+		t.Errorf("pushable = %d, want 3", diff.PushableCount())
+	}
+	// removed d, removed e.png = 2 server-only
+	if diff.ServerOnlyCount() != 2 {
+		t.Errorf("serverOnly = %d, want 2", diff.ServerOnlyCount())
+	}
+}
+
+func TestComputeDiffEmptyServer(t *testing.T) {
+	local := &api.Theme{Templates: []api.ThemeTemplate{tmpl("a", "1")}}
+	localAssets := []LocalAsset{{Key: "b.png", ContentHash: "h"}}
+
+	diff := ComputeDiff(local, localAssets, &api.Theme{})
+
+	if !reflect.DeepEqual(diff.Templates.Added, []string{"a"}) {
+		t.Errorf("templates added = %v", diff.Templates.Added)
+	}
+	if !reflect.DeepEqual(diff.Assets.Added, []string{"b.png"}) {
+		t.Errorf("assets added = %v", diff.Assets.Added)
+	}
+	if diff.ServerOnlyCount() != 0 {
+		t.Errorf("serverOnly = %d, want 0", diff.ServerOnlyCount())
+	}
+}