diff --git a/src/app.zig b/src/app.zig
index ee690e73..3b3772c4 100644
--- a/src/app.zig
+++ b/src/app.zig
@@ -36,6 +36,7 @@ pub const App = struct {
         http_connect_timeout_ms: ?u31 = null,
         http_max_host_open: ?u8 = null,
         http_max_concurrent: ?u8 = null,
+        user_agent: [:0]const u8,
     };
 
     pub fn init(allocator: Allocator, config: Config) !*App {
@@ -53,6 +54,7 @@ pub const App = struct {
             .http_proxy = config.http_proxy,
             .tls_verify_host = config.tls_verify_host,
             .proxy_bearer_token = config.proxy_bearer_token,
+            .user_agent = config.user_agent,
         });
         errdefer http.deinit();
 
diff --git a/src/browser/ScriptManager.zig b/src/browser/ScriptManager.zig
index 7987aa88..e787c971 100644
--- a/src/browser/ScriptManager.zig
+++ b/src/browser/ScriptManager.zig
@@ -205,7 +205,7 @@ pub fn addFromElement(self: *ScriptManager, element: *parser.Element) !void {
 
     errdefer pending_script.deinit();
 
-    var headers = try Http.Headers.init();
+    var headers = try self.client.newHeaders();
     try page.requestCookie(.{}).headersForRequest(page.arena, remote_url.?, &headers);
 
     try self.client.request(.{
@@ -273,7 +273,7 @@ pub fn blockingGet(self: *ScriptManager, url: [:0]const u8) !BlockingResult {
         .buffer_pool = &self.buffer_pool,
     };
 
-    var headers = try Http.Headers.init();
+    var headers = try self.client.newHeaders();
     try self.page.requestCookie(.{}).headersForRequest(self.page.arena, url, &headers);
 
     var client = self.client;
diff --git a/src/browser/page.zig b/src/browser/page.zig
index ae426d21..fca79144 100644
--- a/src/browser/page.zig
+++ b/src/browser/page.zig
@@ -548,7 +548,7 @@ pub const Page = struct {
         const owned_url = try self.arena.dupeZ(u8, request_url);
         self.url = try URL.parse(owned_url, null);
 
-        var headers = try Http.Headers.init();
+        var headers = try self.http_client.newHeaders();
         if (opts.header) |hdr| try headers.add(hdr);
         try self.requestCookie(.{ .is_navigation = true }).headersForRequest(self.arena, owned_url, &headers);
 
diff --git a/src/browser/xhr/xhr.zig b/src/browser/xhr/xhr.zig
index 3117e9e9..f374ed6d 100644
--- a/src/browser/xhr/xhr.zig
+++ b/src/browser/xhr/xhr.zig
@@ -370,7 +370,7 @@ pub const XMLHttpRequest = struct {
             }
         }
 
-        var headers = try Http.Headers.init();
+        var headers = try page.http_client.newHeaders();
         for (self.headers.items) |hdr| {
             try headers.add(hdr);
         }
diff --git a/src/http/Client.zig b/src/http/Client.zig
index 11e8512d..e603ae9b 100644
--- a/src/http/Client.zig
+++ b/src/http/Client.zig
@@ -96,6 +96,9 @@ notification: ?*Notification = null,
 // restoring, this originally-configured value is what it goes to.
 http_proxy: ?[:0]const u8 = null,
 
+// The complete user-agent header line
+user_agent: [:0]const u8,
+
 // libcurl can monitor arbitrary sockets. Currently, we ever [maybe] want to
 // monitor the CDP client socket, so we've done the simplest thing possible
 // by having this single optional field
@@ -130,6 +133,7 @@ pub fn init(allocator: Allocator, ca_blob: ?c.curl_blob, opts: Http.Opts) !*Clie
         .blocking = blocking,
         .allocator = allocator,
         .http_proxy = opts.http_proxy,
+        .user_agent = opts.user_agent,
         .transfer_pool = transfer_pool,
     };
 
@@ -147,6 +151,10 @@ pub fn deinit(self: *Client) void {
     self.allocator.destroy(self);
 }
 
+pub fn newHeaders(self: *const Client) !Http.Headers {
+    return Http.Headers.init(self.user_agent);
+}
+
 pub fn abort(self: *Client) void {
     while (self.handles.in_use.first) |node| {
         const handle: *Handle = @fieldParentPtr("node", node);
@@ -796,7 +804,7 @@ pub const Transfer = struct {
         self.req.headers.deinit();
 
         var buf: std.ArrayListUnmanaged(u8) = .empty;
-        var new_headers = try Http.Headers.init();
+        var new_headers = try self.client.newHeaders();
         for (headers) |hdr| {
             // safe to re-use this buffer, because Headers.add because curl copies
             // the value we pass into curl_slist_append.
diff --git a/src/http/Http.zig b/src/http/Http.zig
index 21b88469..5de4d859 100644
--- a/src/http/Http.zig
+++ b/src/http/Http.zig
@@ -102,12 +102,17 @@ pub fn newConnection(self: *Http) !Connection {
     return Connection.init(self.ca_blob, &self.opts);
 }
 
+pub fn newHeaders(self: *const Http) Headers {
+    return Headers.init(self.opts.user_agent);
+}
+
 pub const Connection = struct {
     easy: *c.CURL,
     opts: Connection.Opts,
 
     const Opts = struct {
         proxy_bearer_token: ?[:0]const u8,
+        user_agent: [:0]const u8,
     };
 
     // pointer to opts is not stable, don't hold a reference to it!
@@ -168,6 +173,7 @@ pub const Connection = struct {
         return .{
             .easy = easy,
             .opts = .{
+                .user_agent = opts.user_agent,
                 .proxy_bearer_token = opts.proxy_bearer_token,
             },
         };
@@ -230,7 +236,7 @@ pub const Connection = struct {
     pub fn request(self: *const Connection) !u16 {
         const easy = self.easy;
 
-        var header_list = try Headers.init();
+        var header_list = try Headers.init(self.opts.user_agent);
         defer header_list.deinit();
         try self.secretHeaders(&header_list);
         try errorCheck(c.curl_easy_setopt(easy, c.CURLOPT_HTTPHEADER, header_list.headers));
@@ -259,8 +265,8 @@ pub const Headers = struct {
     headers: *c.curl_slist,
     cookies: ?[*c]const u8,
 
-    pub fn init() !Headers {
-        const header_list = c.curl_slist_append(null, "User-Agent: Lightpanda/1.0");
+    pub fn init(user_agent: [:0]const u8) !Headers {
+        const header_list = c.curl_slist_append(null, user_agent);
         if (header_list == null) return error.OutOfMemory;
         return .{ .headers = header_list, .cookies = null };
     }
@@ -337,6 +343,7 @@ pub const Opts = struct {
     tls_verify_host: bool = true,
     http_proxy: ?[:0]const u8 = null,
     proxy_bearer_token: ?[:0]const u8 = null,
+    user_agent: [:0]const u8,
 };
 
 pub const Method = enum {
diff --git a/src/main.zig b/src/main.zig
index 7485e8fa..fdfc9142 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -108,6 +108,14 @@ fn run(alloc: Allocator) !void {
         log.opts.filter_scopes = lfs;
     }
 
+    const user_agent = blk: {
+        const USER_AGENT = "User-Agent: Lightpanda/1.0";
+        if (args.userAgentSuffix()) |suffix| {
+            break :blk try std.fmt.allocPrintSentinel(args_arena.allocator(), "{s} {s}", .{ USER_AGENT, suffix }, 0);
+        }
+        break :blk USER_AGENT;
+    };
+
     // _app is global to handle graceful shutdown.
     _app = try App.init(alloc, .{
         .run_mode = args.mode,
@@ -118,6 +126,7 @@ fn run(alloc: Allocator) !void {
         .http_connect_timeout_ms = args.httpConnectTiemout(),
         .http_max_host_open = args.httpMaxHostOpen(),
         .http_max_concurrent = args.httpMaxConcurrent(),
+        .user_agent = user_agent,
     });
 
     const app = _app.?;
@@ -260,6 +269,13 @@ const Command = struct {
         };
     }
 
+    fn userAgentSuffix(self: *const Command) ?[]const u8 {
+        return switch (self.mode) {
+            inline .serve, .fetch => |opts| opts.common.user_agent_suffix,
+            else => unreachable,
+        };
+    }
+
     const Mode = union(App.RunMode) {
         help: bool, // false when being printed because of an error
         fetch: Fetch,
@@ -293,6 +309,7 @@ const Command = struct {
         log_level: ?log.Level = null,
         log_format: ?log.Format = null,
         log_filter_scopes: ?[]log.Scope = null,
+        user_agent_suffix: ?[]const u8 = null,
     };
 
     fn printUsageAndExit(self: *const Command, success: bool) void {
@@ -339,6 +356,9 @@ const Command = struct {
             \\                Defaults to
         ++ (if (builtin.mode == .Debug) " pretty." else " logfmt.") ++
             \\
+            \\ --user_agent_suffix
+            \\                Suffix to append to the Lightpanda/X.Y User-Agent
+            \\
         ;
 
         //                                                                     MAX_HELP_LEN|
@@ -713,6 +733,21 @@ fn parseCommonArg(
         return true;
     }
 
+    if (std.mem.eql(u8, "--user_agent_suffix", opt)) {
+        const str = args.next() orelse {
+            log.fatal(.app, "missing argument value", .{ .arg = "--user_agent_suffix" });
+            return error.InvalidArgument;
+        };
+        for (str) |c| {
+            if (!std.ascii.isPrint(c)) {
+                log.fatal(.app, "not printable character", .{ .arg = "--user_agent_suffix" });
+                return error.InvalidArgument;
+            }
+        }
+        common.user_agent_suffix = try allocator.dupe(u8, str);
+        return true;
+    }
+
     return false;
 }
 
diff --git a/src/testing.zig b/src/testing.zig
index d8c894ce..1eac2f22 100644
--- a/src/testing.zig
+++ b/src/testing.zig
@@ -493,6 +493,7 @@ pub fn setup() !void {
     test_app = try App.init(gpa.allocator(), .{
         .run_mode = .serve,
         .tls_verify_host = false,
+        .user_agent = "User-Agent: Lightpanda/1.0 internal-tester",
     });
     errdefer test_app.deinit();