diff --git a/cmd/sketch/main.go b/cmd/sketch/main.go
index 9d8023c..a2c9f52 100644
--- a/cmd/sketch/main.go
+++ b/cmd/sketch/main.go
@@ -217,6 +217,7 @@
 	outsideHTTP         string
 	branchPrefix        string
 	sshConnectionString string
+	subtraceToken       string
 }
 
 // parseCLIFlags parses all command-line flags and returns a CLIFlags struct
@@ -276,6 +277,7 @@
 
 	// Internal flags for development/debugging
 	internalFlags.StringVar(&flags.dumpDist, "dump-dist", "", "(internal) dump embedded /dist/ filesystem to specified directory and exit")
+	internalFlags.StringVar(&flags.subtraceToken, "subtrace-token", "", "(development) run sketch under subtrace.dev with the provided token")
 
 	// Custom usage function that shows only user-visible flags by default
 	userFlags.Usage = func() {
@@ -415,6 +417,7 @@
 		MaxDollars:     flags.maxDollars,
 		BranchPrefix:   flags.branchPrefix,
 		LinkToGitHub:   flags.linkToGitHub,
+		SubtraceToken:  flags.subtraceToken,
 	}
 
 	if err := dockerimg.LaunchContainer(ctx, config); err != nil {
diff --git a/dockerimg/dockerimg.go b/dockerimg/dockerimg.go
index e708745..e207904 100644
--- a/dockerimg/dockerimg.go
+++ b/dockerimg/dockerimg.go
@@ -124,6 +124,9 @@
 
 	// LinkToGitHub enables GitHub branch linking in UI
 	LinkToGitHub bool
+
+	// SubtraceToken enables running sketch under subtrace.dev (development only)
+	SubtraceToken string
 }
 
 // LaunchContainer creates a docker container for a project, installs sketch and opens a connection to it.
@@ -254,6 +257,14 @@
 
 	fmt.Printf("📦 running in container %s\n", cntrName)
 
+	// Setup subtrace if token is provided (development only) - after container creation, before start
+	if config.SubtraceToken != "" {
+		fmt.Println("🔍 Setting up subtrace (development only)")
+		if err := setupSubtraceBeforeStart(ctx, cntrName, config.SubtraceToken); err != nil {
+			return fmt.Errorf("failed to setup subtrace: %w", err)
+		}
+	}
+
 	// Start the sketch container
 	if out, err := combinedOutput(ctx, "docker", "start", cntrName); err != nil {
 		return fmt.Errorf("docker start: %s, %w", out, err)
@@ -543,16 +554,29 @@
 	}
 	cmdArgs = append(cmdArgs, "--security-opt", "seccomp="+seccompPath)
 
+	// Add subtrace environment variable if token is provided
+	if config.SubtraceToken != "" {
+		cmdArgs = append(cmdArgs, "-e", "SUBTRACE_TOKEN="+config.SubtraceToken)
+		cmdArgs = append(cmdArgs, "-e", "SUBTRACE_HTTP2=1")
+	}
+
 	// Add volume mounts if specified
 	for _, mount := range config.Mounts {
 		if mount != "" {
 			cmdArgs = append(cmdArgs, "-v", mount)
 		}
 	}
-	cmdArgs = append(
-		cmdArgs,
-		imgName,
-		"/bin/sketch",
+	cmdArgs = append(cmdArgs, imgName)
+
+	// Add command: either [sketch] or [subtrace run -- sketch]
+	if config.SubtraceToken != "" {
+		cmdArgs = append(cmdArgs, "/usr/local/bin/subtrace", "run", "--", "/bin/sketch")
+	} else {
+		cmdArgs = append(cmdArgs, "/bin/sketch")
+	}
+
+	// Add all sketch arguments
+	cmdArgs = append(cmdArgs,
 		"-unsafe",
 		"-addr=:80",
 		"-session-id="+config.SessionID,
diff --git a/dockerimg/subtrace.go b/dockerimg/subtrace.go
new file mode 100644
index 0000000..c6433b0
--- /dev/null
+++ b/dockerimg/subtrace.go
@@ -0,0 +1,88 @@
+package dockerimg
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+// downloadSubtrace downloads the subtrace binary for the given architecture
+// and caches it in ~/.cache/sketch/subtrace-{platform}-{arch}
+func downloadSubtrace(ctx context.Context, platform, arch string) (string, error) {
+	_ = ctx // ctx is reserved for future timeout/cancellation support
+	homeDir, err := os.UserHomeDir()
+	if err != nil {
+		return "", fmt.Errorf("failed to get home directory: %w", err)
+	}
+
+	cacheDir := filepath.Join(homeDir, ".cache", "sketch")
+	if err := os.MkdirAll(cacheDir, 0o755); err != nil {
+		return "", fmt.Errorf("failed to create cache directory: %w", err)
+	}
+
+	binaryName := fmt.Sprintf("subtrace-%s-%s", platform, arch)
+	binaryPath := filepath.Join(cacheDir, binaryName)
+
+	// Check if the binary already exists
+	if _, err := os.Stat(binaryPath); err == nil {
+		// Binary exists, return the path
+		return binaryPath, nil
+	}
+
+	// Download the binary
+	downloadURL := fmt.Sprintf("https://subtrace.dev/download/latest/%s/%s/subtrace", platform, arch)
+
+	resp, err := http.Get(downloadURL)
+	if err != nil {
+		return "", fmt.Errorf("failed to download subtrace from %s: %w", downloadURL, err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("failed to download subtrace: HTTP %d", resp.StatusCode)
+	}
+
+	// Create the binary file
+	file, err := os.Create(binaryPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to create subtrace binary file: %w", err)
+	}
+	defer file.Close()
+
+	// Copy the downloaded content to the file
+	_, err = io.Copy(file, resp.Body)
+	if err != nil {
+		return "", fmt.Errorf("failed to write subtrace binary: %w", err)
+	}
+
+	// Make the binary executable
+	if err := os.Chmod(binaryPath, 0o755); err != nil {
+		return "", fmt.Errorf("failed to make subtrace binary executable: %w", err)
+	}
+
+	return binaryPath, nil
+}
+
+// setupSubtraceBeforeStart downloads subtrace and uploads it to the container before it starts
+func setupSubtraceBeforeStart(ctx context.Context, cntrName, subtraceToken string) error {
+	if subtraceToken == "" {
+		return nil
+	}
+
+	// Download subtrace binary
+	subtracePath, err := downloadSubtrace(ctx, "linux", runtime.GOARCH)
+	if err != nil {
+		return fmt.Errorf("failed to download subtrace: %w", err)
+	}
+
+	// Copy subtrace binary to the container (container exists but isn't started)
+	if out, err := combinedOutput(ctx, "docker", "cp", subtracePath, cntrName+":/usr/local/bin/subtrace"); err != nil {
+		return fmt.Errorf("failed to copy subtrace to container: %s: %w", out, err)
+	}
+
+	return nil
+}