diff --git a/backend/test/backend_tests/rpc_file_branch_test.clj b/backend/test/backend_tests/rpc_file_branch_test.clj
index a4d84a42dc..fccb45e45d 100644
--- a/backend/test/backend_tests/rpc_file_branch_test.clj
+++ b/backend/test/backend_tests/rpc_file_branch_test.clj
@@ -648,6 +648,66 @@
                   :features cfeat/supported-features
                   :changes [change]})))
 
+(def ^:private file-plugin-change
+  {:type :set-plugin-data :object-type :file :namespace :my-plugin :key "foo" :value "bar"})
+
+(def ^:private base-font-size-change
+  {:type :set-base-font-size :base-font-size "20px"})
+
+(t/deftest merge-applies-file-level-changes
+  (with-redefs [cf/flags (conj cf/flags :branching)]
+    (let [profile (th/create-profile* 1 {:is-active true})
+          file    (th/create-file* 1 {:profile-id (:id profile)
+                                      :project-id (:default-project-id profile)})
+          main-data (fn []
+                      (-> (th/command! {::th/type :get-file
+                                        ::rpc/profile-id (:id profile)
+                                        :id (:id file)})
+                          :result :data))]
+      (doseq [[label change landed?]
+              [["file plugin data" file-plugin-change
+                #(= "bar" (get-in % [:plugin-data :my-plugin "foo"]))]
+               ["base font size" base-font-size-change
+                #(= "20px" (get-in % [:options :base-font-size]))]]]
+        (t/testing label
+          (let [create (:result (th/command! {::th/type :create-file-branch
+                                              ::rpc/profile-id (:id profile)
+                                              :file-id (:id file)
+                                              :name label}))]
+            (t/is (nil? (:error (apply-change* profile (:branch-file-id create) change))))
+            (let [info (:result (th/command! {::th/type :get-file-branch-info
+                                              ::rpc/profile-id (:id profile)
+                                              :file-id (:branch-file-id create)}))]
+              (t/is (= [1 0 0] ((juxt :ahead :behind :conflicts) info))))
+            (let [out (th/command! {::th/type :merge-file-branch
+                                    ::rpc/profile-id (:id profile)
+                                    :branch-id (:id create)})]
+              (t/is (nil? (:error out)))
+              (t/is (= :merged (-> out :result :status))))
+            (t/is (landed? (main-data)))))))))
+
+(t/deftest merge-reports-file-level-conflicts
+  (with-redefs [cf/flags (conj cf/flags :branching)]
+    (let [profile (th/create-profile* 1 {:is-active true})
+          file    (th/create-file* 1 {:profile-id (:id profile)
+                                      :project-id (:default-project-id profile)})
+          create  (:result (th/command! {::th/type :create-file-branch
+                                         ::rpc/profile-id (:id profile)
+                                         :file-id (:id file)
+                                         :name "b"}))]
+      (apply-change* profile (:branch-file-id create) file-plugin-change)
+      (apply-change* profile (:branch-file-id create) base-font-size-change)
+      (apply-change* profile (:id file) (assoc file-plugin-change :value "main"))
+      (apply-change* profile (:id file) (assoc base-font-size-change :base-font-size "18px"))
+      (let [info (:result (th/command! {::th/type :get-file-branch-info
+                                        ::rpc/profile-id (:id profile)
+                                        :file-id (:branch-file-id create)}))]
+        (t/is (= 2 (:conflicts info))))
+      (let [out (th/command! {::th/type :merge-file-branch
+                              ::rpc/profile-id (:id profile)
+                              :branch-id (:id create)})]
+        (t/is (= :conflicts (-> out :result :status)))))))
+
 (t/deftest merge-deletes-branch-by-default-and-releases-base
   (with-redefs [cf/flags (conj cf/flags :branching)]
     (let [profile (th/create-profile* 1 {:is-active true})
diff --git a/common/src/app/common/files/branch_merge.cljc b/common/src/app/common/files/branch_merge.cljc
index 02d48a243e..262d3785aa 100644
--- a/common/src/app/common/files/branch_merge.cljc
+++ b/common/src/app/common/files/branch_merge.cljc
@@ -23,6 +23,7 @@
    [app.common.data :as d]
    [app.common.files.helpers :as cfh]
    [app.common.types.component :as ctk]
+   [app.common.types.file :as ctf]
    [app.common.types.pages-list :as ctpl]
    [app.common.types.tokens-lib :as ctob]
    [app.common.types.tokens-status :as ctos]
@@ -414,6 +415,19 @@
               (transient {})
               (or pd {}))))
 
+(defn- file-options
+  "File options the merge carries, keyed by option name. An unset base
+  font size reads as the default, so a side that never set it does not
+  differ from a side that set the default explicitly."
+  [data]
+  {:base-font-size (ctf/get-base-font-size data)})
+
+(defn- set-option-change
+  "Change op that sets file option `option` to `value`."
+  [option value]
+  (case option
+    :base-font-size {:type :set-base-font-size :base-font-size value}))
+
 ;; --- Shape tree ---
 ;;
 ;; `three-way-entities` classifies shapes one by one, while containment
@@ -1248,6 +1262,14 @@
                                       {:kind :component})
                   (three-way-entities (:media base) (:media theirs) (:media ours)
                                       {:kind :media})
+                  ;; file-level plugin data and options: kinds of their own,
+                  ;; or a branch that changes only them merges as a no-op
+                  (three-way-entities (flatten-plugin-data (:plugin-data base))
+                                      (flatten-plugin-data (:plugin-data theirs))
+                                      (flatten-plugin-data (:plugin-data ours))
+                                      {:kind :file-plugin})
+                  (three-way-entities (file-options base) (file-options theirs) (file-options ours)
+                                      {:kind :file-option})
                   (diff-pages base theirs ours only-pages dir)
                   (diff-tokens base theirs ours)]
         {:keys [changes conflicts]} (merge-results results)
@@ -1326,7 +1348,8 @@
 (def ^:private mergeable-kinds
   #{:color :typography :media :shape :token :token-set :token-set-rename :token-set-order
     :token-theme :token-active-themes :token-active-sets
-    :page :page-order :page-guide :page-flow :page-grid :page-plugin :component})
+    :page :page-order :page-guide :page-flow :page-grid :page-plugin :component
+    :file-plugin :file-option})
 
 (defn unsupported-kinds
   "Set of change kinds present in `changes` that `compute-changes`
@@ -1937,6 +1960,21 @@
                       (fn [_ o] {:type :mod-media :object o})
                       (fn [id] {:type :del-media :id id}))
 
+         ;; file-level plugin-data (flattened to [ns key] -> value)
+         file-plugins (flat :file-plugin {}
+                            (flatten-plugin-data (:plugin-data base))
+                            (flatten-plugin-data (:plugin-data main))
+                            (flatten-plugin-data (:plugin-data branch))
+                            (fn [[ns k] v] {:type :set-plugin-data :object-type :file :namespace ns :key k :value v})
+                            (fn [[ns k] v] {:type :set-plugin-data :object-type :file :namespace ns :key k :value v})
+                            (fn [[ns k]] {:type :set-plugin-data :object-type :file :namespace ns :key k :value nil}))
+
+         ;; file options: every side carries every option (`file-options`
+         ;; fills the default), so no option is ever added or deleted
+         file-opts (flat :file-option {}
+                         (file-options base) (file-options main) (file-options branch)
+                         set-option-change set-option-change (fn [_] nil))
+
          ;; pages: add (full page incl. objects) / delete + rename (mod-page)
          bpi (:pages-index base) mpi (:pages-index main) opi (:pages-index branch)
          bpids (set (keys bpi)) mpids (set (keys mpi)) opids (set (keys opi))
@@ -2194,7 +2232,7 @@
       ;; objects (still on the page) before del-obj removes them
       :changes     (vec (concat page-presence components shapes page-meta-changes
                                 page-guides page-flows page-grids page-plugins page-order-changes
-                                colors typos media
+                                colors typos media file-plugins (filterv some? file-opts)
                                 set-presence set-rename-changes set-order-changes
                                 token-vals themes
                                 active-changes))})))
diff --git a/common/test/common_tests/files_branch_merge_test.cljc b/common/test/common_tests/files_branch_merge_test.cljc
index 90d0295f1f..633daaf2a5 100644
--- a/common/test/common_tests/files_branch_merge_test.cljc
+++ b/common/test/common_tests/files_branch_merge_test.cljc
@@ -670,6 +670,96 @@
     (let [data' (cfc/process-changes base changes)]
       (t/is (= "bar" (get-in data' [:pages-index pid :plugin-data :my-plugin "foo"]))))))
 
+;; --- file-level plugin data and options
+
+(defn- file-level-data
+  [& {:keys [plugin-data base-font-size]}]
+  (let [pid (uuid/custom 0 1)]
+    (cond-> (pages-data {pid {:id pid :name "P" :objects {}}} [pid])
+      (some? plugin-data)    (assoc :plugin-data plugin-data)
+      (some? base-font-size) (assoc-in [:options :base-font-size] base-font-size))))
+
+(t/deftest compute-merge-file-plugin-data
+  (let [base   (file-level-data)
+        branch (file-level-data :plugin-data {:my-plugin {"foo" "bar"}})
+        r      (bm/compute-merge base base branch :branch->main)
+        c      (first (:changes r))]
+    (t/is (= {:added 1 :modified 0 :deleted 0 :conflicts 0} (:stats r)))
+    (t/is (= :file-plugin (:kind c)))
+    (t/is (= [:my-plugin "foo"] (:id c)))))
+
+(t/deftest compute-merge-file-base-font-size
+  (let [base   (file-level-data :base-font-size "16px")
+        branch (file-level-data :base-font-size "20px")
+        r      (bm/compute-merge base base branch :branch->main)
+        c      (first (:changes r))]
+    (t/is (= {:added 0 :modified 1 :deleted 0 :conflicts 0} (:stats r)))
+    (t/is (= :file-option (:kind c)))
+    (t/is (= :base-font-size (:id c)))))
+
+(t/deftest compute-merge-file-base-font-size-absent-is-the-default
+  (let [base   (file-level-data)
+        branch (file-level-data :base-font-size "16px")]
+    (t/is (empty? (:changes (bm/compute-merge base base branch :branch->main))))))
+
+(t/deftest compute-merge-file-level-conflicts
+  (let [base   (file-level-data :plugin-data {:my-plugin {"foo" "a"}} :base-font-size "16px")
+        main   (file-level-data :plugin-data {:my-plugin {"foo" "b"}} :base-font-size "18px")
+        branch (file-level-data :plugin-data {:my-plugin {"foo" "c"}} :base-font-size "20px")
+        r      (bm/compute-merge base main branch :branch->main)]
+    (t/is (= 2 (-> r :stats :conflicts)))
+    (t/is (= #{:file-plugin :file-option} (set (map :kind (:conflicts r)))))
+    (t/is (every? #(= :modify-modify (:reason %)) (:conflicts r)))
+    (t/is (= #{["b" "c"] ["18px" "20px"]}
+             (set (map (juxt :main :branch) (:conflicts r)))))))
+
+(t/deftest compute-changes-file-plugin-data
+  (let [base   (file-level-data :plugin-data {:my-plugin {"gone" "x"}})
+        branch (file-level-data :plugin-data {:my-plugin {"foo" "bar"}})
+        {:keys [changes unsupported]} (bm/compute-changes base base branch)
+        sets   (filter #(= :set-plugin-data (:type %)) changes)]
+    (t/is (empty? unsupported))
+    (t/is (= #{{:type :set-plugin-data :object-type :file
+                :namespace :my-plugin :key "foo" :value "bar"}
+               {:type :set-plugin-data :object-type :file
+                :namespace :my-plugin :key "gone" :value nil}}
+             (set sets)))
+    (let [data' (cfc/process-changes base changes)]
+      (t/is (= {"foo" "bar"} (get-in data' [:plugin-data :my-plugin]))))))
+
+(t/deftest compute-changes-file-base-font-size
+  (let [base   (file-level-data :base-font-size "16px")
+        branch (file-level-data :base-font-size "20px")
+        {:keys [changes unsupported]} (bm/compute-changes base base branch)]
+    (t/is (empty? unsupported))
+    (t/is (= [{:type :set-base-font-size :base-font-size "20px"}] changes))
+    (let [data' (cfc/process-changes base changes)]
+      (t/is (= "20px" (get-in data' [:options :base-font-size]))))))
+
+(t/deftest compute-changes-file-level-conflict-resolutions
+  (let [base   (file-level-data :plugin-data {:my-plugin {"foo" "a"}} :base-font-size "16px")
+        main   (file-level-data :plugin-data {:my-plugin {"foo" "b"}} :base-font-size "18px")
+        branch (file-level-data :plugin-data {:my-plugin {"foo" "c"}} :base-font-size "20px")
+        apply* (fn [resolutions]
+                 (cfc/process-changes main (:changes (bm/compute-changes base main branch resolutions))))]
+    (t/testing "unresolved: main keeps its values"
+      (let [data' (apply* {})]
+        (t/is (= "b" (get-in data' [:plugin-data :my-plugin "foo"])))
+        (t/is (= "18px" (get-in data' [:options :base-font-size])))))
+    (t/testing "resolved to the branch: the branch values land"
+      (let [data' (apply* {[:my-plugin "foo"] :branch :base-font-size :branch})]
+        (t/is (= "c" (get-in data' [:plugin-data :my-plugin "foo"])))
+        (t/is (= "20px" (get-in data' [:options :base-font-size])))))))
+
+(t/deftest compute-changes-file-level-update-from-main
+  (let [base   (file-level-data)
+        main   (file-level-data :plugin-data {:my-plugin {"foo" "bar"}} :base-font-size "20px")
+        r      (bm/compute-merge base main base :main->branch)
+        data'  (cfc/process-changes base (:changes (bm/compute-changes base base main {} r)))]
+    (t/is (= 2 (count (:changes r))))
+    (t/is (= "bar" (get-in data' [:plugin-data :my-plugin "foo"])))
+    (t/is (= "20px" (get-in data' [:options :base-font-size])))))
+
 ;; --- components
 
 (t/deftest compute-changes-component-add
diff --git a/frontend/src/app/main/ui/workspace/sidebar/branches.cljs b/frontend/src/app/main/ui/workspace/sidebar/branches.cljs
index 2f3d36809f..b3fede1741 100644
--- a/frontend/src/app/main/ui/workspace/sidebar/branches.cljs
+++ b/frontend/src/app/main/ui/workspace/sidebar/branches.cljs
@@ -65,6 +65,8 @@
    :page-flow           i/document
    :page-grid           i/document
    :page-plugin         i/document
+   :file-plugin         i/document
+   :file-option         i/document
    :token               i/tokens
    :token-set           i/tokens
    :token-set-rename    i/tokens