diff --git a/src/clj/rems/main.clj b/src/clj/rems/main.clj
index 3de05890d..4b7365fe6 100644
--- a/src/clj/rems/main.clj
+++ b/src/clj/rems/main.clj
@@ -10,6 +10,7 @@
             [mount.core :as mount]
             [rems.application.search :as search]
             [rems.common.git :as git]
+            [rems.common.util :refer [not-blank]]
             [rems.config :refer [env]]
             [rems.db.api-key]
             [rems.db.applications]
@@ -24,6 +25,7 @@
             [rems.service.fix-userid]
             [rems.service.test-data :as test-data]
             [rems.service.users]
+            [rems.user-simulator]
             [rems.validate :as validate])
   (:import [sun.misc Signal SignalHandler]
            [org.eclipse.jetty.server.handler.gzip GzipHandler])
@@ -146,7 +148,10 @@
         Example regex: /api/applications/[0-9]+/?
      \"api-key allow-all <api-key>\" -- clears the allowed method/path whitelist.
         An empty list means all methods and paths are allowed.
-     \"rename-user <old-userid> <new-userid>\" -- change a user's identity from old to new"
+     \"rename-user <old-userid> <new-userid>\" -- change a user's identity from old to new
+     \"user-simulator <url> <users>\" -- start user simulator that runs concurrent headless browser instances against target REMS.
+        <url> is target REMS (e.g. http://localhost:3000).
+        <users> is an comma-separated list of user ids (e.g. alice,elsa,frank). Each user is simulated in separate thread."
   [& args]
   (try
     (exit-on-signals!)
@@ -300,6 +305,13 @@
                     (rems.service.fix-userid/fix-all old-userid new-userid simulate?)
                     (println "Finished.\n\nConsider rebooting the server process next to refresh all the caches, most importantly the application cache.")))))
 
+          "user-simulator"
+          (let [[_ url users] args]
+            (rems.user-simulator/start! {:url url
+                                         :users (when (not-blank users)
+                                                  (mapv str/trim (str/split users #",")))})
+            (.addShutdownHook (Runtime/getRuntime) (Thread. rems.user-simulator/stop!)))
+
           (do
             (println "Unrecognized argument:" (first args))
             (usage)
diff --git a/src/clj/rems/user_simulator.clj b/src/clj/rems/user_simulator.clj
new file mode 100644
index 000000000..7a9ce9157
--- /dev/null
+++ b/src/clj/rems/user_simulator.clj
@@ -0,0 +1,217 @@
+(ns rems.user-simulator
+  "Namespace for simulating actual user interactions with in REMS, allowing
+   automated testing of user behavior. Simulations run in a headless browser
+   using etaoin with chromedriver, and can be configured via the command line
+   interface (CLI). Various user scenarios are implemented as functions in this
+   namespace, enabling flexible testing of different workflows. Multiple
+   simulations can run concurrently to test system performance and user load.
+   
+   User simulator can be started from CLI with e.g. Leiningen:
+   - `lein run user-simulator` (uses default values), or
+   - `lein run user-simulator http://localhost:3000/ alice,elsa,frank` when replacing default values"
+  (:require [clj-http.client :as http]
+            [clojure.pprint]
+            [clojure.string :as str]
+            [clojure.tools.logging.readable :as logr]
+            [etaoin.api :as et]
+            [mount.core :as mount]
+            [muuntaja.core :as muuntaja]
+            [rems.browser-test-util :as btu]
+            [rems.common.util :refer [rand-nth*]]
+            [rems.config]
+            [rems.concurrency :as concurrency]
+            [rems.json :as json]
+            [rems.logging :refer [with-mdc]]))
+
+
+;;; threadpool
+
+
+(def ^:private thread-pool (atom nil))
+
+(defn- submit-all [& fns]
+  (let [pool (or @thread-pool
+                 (reset! thread-pool (concurrency/cached-thread-pool {:thread-prefix "user-simulator"})))]
+    (concurrency/submit! pool fns)))
+
+(def task-counter (atom 0))
+(def restart-queue (atom []))
+
+(defn create-simulator-task [{:keys [actions url user-id] :as opts}]
+  (logr/info #'create-simulator-task opts)
+  (binding [btu/*test-context* (atom (assoc (btu/create-test-context)
+                                            :url url))
+            btu/screenshot (constantly nil)
+            btu/screenshot-element (constantly nil)
+            btu/check-axe (constantly nil)
+            btu/postmortem-handler (constantly nil)]
+    (bound-fn simulate-user []
+      (try
+        (logr/info "Simulator thread starting")
+        (btu/init-driver! :chrome (btu/get-server-url))
+        (btu/context-assoc! :user-id user-id)
+
+        (while true
+          (Thread/sleep (+ 200 (rand-int 300)))
+
+          (when (btu/running?)
+            (let [action-var (rand-nth actions)
+                  action (var-get action-var)
+                  task-id (swap! task-counter inc)]
+              (btu/context-assoc! :task-id task-id)
+              (with-mdc {:userid user-id
+                         :request-id task-id}
+                (et/delete-cookies (btu/get-driver))
+                (btu/go (btu/get-server-url))
+                (et/refresh (btu/get-driver))
+                (btu/scroll-and-click [{:css ".language-switcher"} {:fn/text "EN"}]) ; make sure language is stable
+                (action)))))
+
+        (catch InterruptedException e
+          (.interrupt (Thread/currentThread))
+          (logr/info e "Simulator thread interrupted"))
+        (catch Throwable t
+          (logr/error t "Internal error" (with-out-str
+                                           (clojure.pprint/pprint (merge {::context @(btu/test-ctx)}
+                                                                         (ex-data t)))))
+          (swap! restart-queue conj opts))
+        (finally
+          (logr/info "Simulator thread shutting down")
+          (some-> (btu/get-driver)
+                  et/stop-driver))))))
+
+
+;;; api utils
+
+
+(defn- parse-transit [x]
+  (muuntaja/decode json/muuntaja "application/transit+json" x))
+
+(defn- join-url [base path]
+  (let [base (cond-> base
+               (str/ends-with? base "/")
+               (subs 0 (dec (count base))))
+        path (cond-> path
+               (str/starts-with? path "/")
+               (subs 1))]
+    (str base "/" path)))
+
+(comment
+  (= "http://localhost:3000/api/applications"
+     (join-url "http://localhost:3000" "api/applications")
+     (join-url "http://localhost:3000" "/api/applications")
+     (join-url "http://localhost:3000/" "api/applications")
+     (join-url "http://localhost:3000/" "/api/applications")))
+
+(defn- api-get [path & [{:keys [api-key user-id]}]]
+  (let [url (join-url (btu/get-server-url) path)
+        response (http/get url {:accept :transit+json
+                                :headers {"x-rems-api-key" (or api-key 42)
+                                          "x-rems-user-id" (or user-id (btu/context-getx :user-id))}})]
+    (parse-transit (:body response))))
+
+(defn- query-my-applications []
+  (let [user-id (btu/context-getx :user-id)]
+    (->> (api-get "/api/applications")
+         (filter #(= user-id (get-in % [:application/applicant :userid])))
+         (mapv :application/id))))
+
+
+;;; etaoin utils
+
+
+(defn login-as [username]
+  (btu/go (btu/get-server-url))
+  (btu/scroll-and-click {:css ".login-btn"})
+  (when (btu/visible? :show-special-users) ; sometimes the user is in the hidden part
+    (btu/scroll-and-click :show-special-users))
+  (btu/scroll-and-click [{:css ".users"} {:tag :a :fn/text username}])
+  (btu/wait-visible :logout))
+
+(defn logout []
+  (btu/scroll-and-click :logout)
+  (btu/wait-visible {:css ".login-component"}))
+
+(defn click-navigation-menu [link-text]
+  (btu/scroll-and-click [:big-navbar {:tag :a :fn/text link-text}]))
+
+(defn go-to-application [application-id]
+  (click-navigation-menu "Applications")
+  (btu/wait-visible {:tag :h1 :fn/text "Applications – REMS"})
+  (btu/wait-page-loaded)
+  (btu/scroll-and-click [:my-applications
+                         {:css (format "tr[data-row='%s'] > td.view a" application-id)}])
+  (btu/wait-page-loaded))
+
+
+;;; simulations
+
+
+(defn user-views-applications
+  "Simulation flow where
+   - user logs in,
+   - user visits random application pages (that user is applying for)
+   - user logs out."
+  []
+  (logr/info "login")
+  (login-as (btu/context-getx :user-id))
+  (loop [n 0]
+    (Thread/sleep 1000)
+    (btu/context-assoc! :my-applications (query-my-applications))
+    (btu/context-assoc! :application-id (rand-nth* (btu/context-getx :my-applications)))
+    (cond
+      (>= n 100)
+      (do (logr/info "logout")
+          (logout))
+
+      (not (btu/context-getx :application-id))
+      (do (logr/warnf "No applications found for user %s" (btu/context-getx :user-id))
+          (recur (inc n)))
+
+      :else
+      (let [start (System/currentTimeMillis)]
+        (logr/infof "> view application %s/%s, id %s" n 100 (btu/context-getx :application-id))
+        (go-to-application (btu/context-getx :application-id))
+        (logr/infof "< view application %s/%s, id %s (%sms)" n 100 (- (System/currentTimeMillis) start) (btu/context-getx :application-id))
+        (recur (inc n))))))
+
+
+;;; core logic
+
+
+(def all-actions [#'user-views-applications])
+
+(defn- queue-simulate-tasks! [opts]
+  (assert (seq (:users opts)) "no users to simulate?")
+  (assert (seq (:actions opts)) "no actions to simulate?")
+  (assert (:url opts) "missing target REMS url")
+  (logr/info 'queue-simulate-tasks :start opts)
+  (submit-all (vec (for [user-id (:users opts)
+                         :let [task-opts {:actions (:actions opts)
+                                          :url (:url opts)
+                                          :user-id user-id}]]
+                     (create-simulator-task task-opts))))
+  (add-watch restart-queue :task-daemon (fn [_key q _old-state new-state]
+                                          (when (seq new-state)
+                                            (submit-all (mapv create-simulator-task new-state))
+                                            (reset! q [])))))
+
+(defn start! [& [{:keys [actions url users]}]]
+  (mount/start #'rems.config/env)
+  (queue-simulate-tasks! {:actions (or (seq actions) all-actions)
+                          :url (or url "http://localhost:3000/")
+                          :users (or (seq users) ["alice" "elsa" "frank"])}))
+
+(defn stop! []
+  (remove-watch restart-queue :task-daemon)
+  (some-> @thread-pool concurrency/shutdown-now!))
+
+(comment
+  ;; can also be started from command line, like:
+  ;; "lein run user-simulator http://localhost:3000/ alice,elsa,frank"
+  (start!)
+  (start! {:actions [#'user-views-applications]
+           :url "https://rems-dev.2.rahtiapp.fi/"
+           :users ["alice"]})
+
+  (stop!))
diff --git a/src/cljc/rems/common/util.cljc b/src/cljc/rems/common/util.cljc
index 967bb41af..ae847d749 100644
--- a/src/cljc/rems/common/util.cljc
+++ b/src/cljc/rems/common/util.cljc
@@ -724,3 +724,9 @@
   "Like `clojure.core/range`, but starts from 1 and `end` is inclusive."
   [end]
   (range 1 (inc end)))
+
+(defn rand-nth*
+  "As (rand-nth), but returns nil if (seq coll) is nil."
+  [coll]
+  (some-> (seq coll)
+          (rand-nth)))
diff --git a/test/clj/rems/api/testing.clj b/test/clj/rems/api/testing.clj
index e00617dbc..926f9e668 100644
--- a/test/clj/rems/api/testing.clj
+++ b/test/clj/rems/api/testing.clj
@@ -11,7 +11,6 @@
             [rems.handler :refer :all]
             [rems.locales]
             [rems.middleware]
-            [rems.main]
             [ring.mock.request :refer :all]
             [rems.json :as json]))
 
diff --git a/test/clj/rems/browser_test_util.clj b/test/clj/rems/browser_test_util.clj
index 97710d9a3..738a5cdc2 100644
--- a/test/clj/rems/browser_test_util.clj
+++ b/test/clj/rems/browser_test_util.clj
@@ -21,7 +21,6 @@
             [rems.db.test-data-users :as test-users]
             [rems.service.test-data :as test-data]
             [rems.json :as json]
-            [rems.main]
             [rems.testing-util :refer [get-current-test-name]]
             [rems.util :refer [ensure-empty-directory!]]
             [slingshot.slingshot :refer [try+]])
@@ -58,9 +57,9 @@
 
 (defn context-get [k] (test-ctx :test-data k))
 (defn context-getx [k] (getx (test-ctx :test-data) k))
-(defn context-update! [& args] (apply swap! (test-ctx) update :test-data args))
-(defn context-assoc! [& args] (apply context-update! assoc args))
-(defn context-dissoc! [& args] (apply context-update! dissoc args))
+(defn context-update! [f & args] (apply swap! (test-ctx) update :test-data f args))
+(defn context-assoc! [k v & kvs] (apply context-update! assoc k v kvs))
+(defn context-dissoc! [k & ks] (apply context-update! dissoc k ks))
 
 (defn- ensure-empty-directories! []
   (ensure-empty-directory! (test-ctx :reporting-dir))
@@ -327,7 +326,7 @@
           (get-sequence-number)
           (get-current-test-name)))
 
-(defn screenshot [filename]
+(defn ^:dynamic screenshot [filename]
   (let [driver (get-driver)
         _ (wait-for-idle driver 500)
         full-filename (str (get-file-base) filename ".png")
@@ -355,7 +354,7 @@
     (when need-to-adjust?
       (et/set-window-rect driver window-size))))
 
-(defn screenshot-element [filename q]
+(defn ^:dynamic screenshot-element [filename q]
   (let [full-filename (format "%03d-%s-%s"
                               (get-sequence-number)
                               (get-current-test-name)
@@ -389,6 +388,9 @@
                                   {:explanation (explainer)}))
                          ex)))))
 
+(defn running? []
+  (et/running? (get-driver)))
+
 (defn wrap-etaoin [f]
   (fn [& args] (apply f (get-driver) args)))
 
@@ -581,7 +583,7 @@
                               ['body > div:not(#app)']]
    }).then(callback);")
 
-(defn check-axe
+(defn ^:dynamic check-axe
   "Runs automated accessibility tests using axe.
 
   Returns the test report.
@@ -662,7 +664,7 @@
 (defn autosave-enabled? []
   (get env :enable-autosave false))
 
-(defn postmortem-handler
+(defn ^:dynamic postmortem-handler
   "Simplified version of `etaoin.api/postmortem-handler`"
   [ex]
   (let [driver (get-driver)
diff --git a/test/clj/rems/test_browser.clj b/test/clj/rems/test_browser.clj
index 20ae4792e..6c41e4418 100644
--- a/test/clj/rems/test_browser.clj
+++ b/test/clj/rems/test_browser.clj
@@ -29,7 +29,6 @@
             [rems.db.test-data-helpers :as test-helpers]
             [rems.db.testing :refer [save-cache-statistics!]]
             [rems.db.user-settings]
-            [rems.main]
             [rems.testing-util :refer [with-user with-fake-login-users]]
             [rems.text :refer [localize-time text with-language]]))