diff --git a/cmd/certspotter/main.go b/cmd/certspotter/main.go
index d099a5d..cadcd02 100644
--- a/cmd/certspotter/main.go
+++ b/cmd/certspotter/main.go
@@ -19,11 +19,13 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
+	"runtime"
 	"runtime/debug"
 	"strings"
 	"syscall"
 	"time"
 
+	"software.sslmate.com/src/certspotter/loglist"
 	"software.sslmate.com/src/certspotter/monitor"
 )
 
@@ -103,7 +105,7 @@ func appendFunc(slice *[]string) func(string) error {
 func main() {
 	insecurerand.Seed(time.Now().UnixNano()) // TODO: remove after upgrading to Go 1.20
 
-	// TODO-3: set loglist.UserAgent
+	loglist.UserAgent = fmt.Sprintf("certspotter/%s (%s; %s; %s)", certspotterVersion(), runtime.Version(), runtime.GOOS, runtime.GOARCH)
 
 	var flags struct {
 		batchSize  int // TODO-4: respect this option
diff --git a/loglist/load.go b/loglist/load.go
index 0e94124..11c8e8f 100644
--- a/loglist/load.go
+++ b/loglist/load.go
@@ -21,6 +21,8 @@ import (
 	"time"
 )
 
+var UserAgent = "certspotter"
+
 type ModificationToken struct {
 	etag     string
 	modified time.Time
@@ -70,6 +72,7 @@ func FetchIfModified(ctx context.Context, url string, token *ModificationToken)
 	if err != nil {
 		return nil, nil, err
 	}
+	request.Header.Set("User-Agent", UserAgent)
 	if token != nil {
 		token.setRequestHeaders(request)
 	}