diff --git a/web/lib/potato_mesh/application/federation.rb b/web/lib/potato_mesh/application/federation.rb
index a1d8e58..f256ca8 100644
--- a/web/lib/potato_mesh/application/federation.rb
+++ b/web/lib/potato_mesh/application/federation.rb
@@ -250,6 +250,9 @@ module PotatoMesh
       end
 
       def start_federation_announcer!
+        # Federation broadcasts must not execute when federation support is disabled.
+        return nil unless federation_enabled?
+
         existing = settings.federation_thread
         return existing if existing&.alive?
 
@@ -277,6 +280,9 @@ module PotatoMesh
       #
       # @return [Thread, nil] the thread handling the initial announcement.
       def start_initial_federation_announcement!
+        # Skip the initial broadcast entirely when federation is disabled.
+        return nil unless federation_enabled?
+
         existing = settings.respond_to?(:initial_federation_thread) ? settings.initial_federation_thread : nil
         return existing if existing&.alive?
 
diff --git a/web/lib/potato_mesh/application/routes/api.rb b/web/lib/potato_mesh/application/routes/api.rb
index e59f5f8..a79f183 100644
--- a/web/lib/potato_mesh/application/routes/api.rb
+++ b/web/lib/potato_mesh/application/routes/api.rb
@@ -125,6 +125,9 @@ module PotatoMesh
           end
 
           app.get "/api/instances" do
+            # Prevent the federation catalog from being exposed when federation is disabled.
+            halt 404 unless federation_enabled?
+
             content_type :json
             ensure_self_instance_record!
             payload = load_instances_for_api
diff --git a/web/spec/app_spec.rb b/web/spec/app_spec.rb
index 73d0e12..d88afd1 100644
--- a/web/spec/app_spec.rb
+++ b/web/spec/app_spec.rb
@@ -280,6 +280,40 @@ RSpec.describe "Potato Mesh Sinatra app" do
       expect(result).to be(dummy_thread)
       expect(app.settings.federation_thread).to be(dummy_thread)
     end
+
+    context "when federation is disabled" do
+      around do |example|
+        original = ENV["FEDERATION"]
+        begin
+          ENV["FEDERATION"] = "0"
+          example.run
+        ensure
+          if original.nil?
+            ENV.delete("FEDERATION")
+          else
+            ENV["FEDERATION"] = original
+          end
+        end
+      end
+
+      it "does not start the initial announcement thread" do
+        expect(Thread).not_to receive(:new)
+
+        result = app.start_initial_federation_announcement!
+
+        expect(result).to be_nil
+        expect(app.settings.respond_to?(:initial_federation_thread) ? app.settings.initial_federation_thread : nil).to be_nil
+      end
+
+      it "does not start the recurring announcer thread" do
+        expect(Thread).not_to receive(:new)
+
+        result = app.start_federation_announcer!
+
+        expect(result).to be_nil
+        expect(app.settings.federation_thread).to be_nil
+      end
+    end
   end
 
   before do
@@ -2023,6 +2057,28 @@ RSpec.describe "Potato Mesh Sinatra app" do
         expect(domains).to eq(["duplicate.example"])
       end
     end
+
+    context "when federation is disabled" do
+      around do |example|
+        original = ENV["FEDERATION"]
+        begin
+          ENV["FEDERATION"] = "0"
+          example.run
+        ensure
+          if original.nil?
+            ENV.delete("FEDERATION")
+          else
+            ENV["FEDERATION"] = original
+          end
+        end
+      end
+
+      it "returns 404" do
+        get "/api/instances"
+
+        expect(last_response.status).to eq(404)
+      end
+    end
   end
 
   describe "POST /api/nodes" do