Show and clear split_override cookies from the dashboard

"Force for current user" sets a split_override cookie, but the dashboard
gave no sign it had done so. Because an override is not counted as a
participant unless store_override is set, a pinned experiment reads zero
participants while still rendering an alternative, which looks like the
experiment is broken.

The dashboard now lists the overrides active in the browser at the top of
the page, explains why the numbers can read zero, marks the pinned
alternative in the experiment's table, and can clear them one at a time or
all at once.

The cookie name is now a constant shared by the helper and the dashboard,
instead of being spelled out at each use.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: andrehjr

README.md

@@ -168,6 +168,8 @@ If you have an experiment called `button_color` with alternatives called `red` a
 
 will always have red buttons. This won't be stored in your session or count towards to results, unless you set the `store_override` configuration option.
 
+The dashboard's "Force for current user" button does the same thing for your browser, by setting a `split_override` cookie. Because an override is not counted, an experiment you have pinned can keep reading zero participants. The dashboard lists any overrides active in your browser at the top of the page, and lets you clear them individually or all at once.
+
 In the event you want to disable all tests without having to know the individual experiment names, add a `SPLIT_DISABLE` query parameter.
 
     http://myawesomesite.com?SPLIT_DISABLE=true

lib/split.rb

@@ -30,6 +30,8 @@ module Split
   extend self
   attr_accessor :configuration
 
+  OVERRIDE_COOKIE_NAME = "split_override"
+
   # Accepts:
   #   1. A redis URL (valid for `Redis.new(url: url)`)
   #   2. an options hash compatible with `Redis.new`

lib/split/dashboard.rb

@@ -45,9 +45,21 @@ class Dashboard < Sinatra::Base
       experiment = Split::ExperimentCatalog.find(params[:experiment])
       alternative = Split::Alternative.new(params[:alternative], experiment.name)
 
-      cookies = JSON.parse(request.cookies["split_override"]) rescue {}
-      cookies[experiment.name] = alternative.name
-      response.set_cookie("split_override", { value: cookies.to_json, path: "/" })
+      write_overrides(active_overrides.merge(experiment.name => alternative.name))
+
+      redirect url("/")
+    end
+
+    post "/clear_override" do
+      overrides = active_overrides
+      overrides.delete(params[:experiment])
+      write_overrides(overrides)
+
+      redirect url("/")
+    end
+
+    post "/clear_overrides" do
+      response.delete_cookie(Split::OVERRIDE_COOKIE_NAME, path: "/")
 
       redirect url("/")
     end

lib/split/dashboard/helpers.rb

@@ -1,13 +1,32 @@
 # frozen_string_literal: true
 
 require "bigdecimal"
+require "json"
 
 module Split
   module DashboardHelpers
     def h(text)
       Rack::Utils.escape_html(text)
     end
 
+    def active_overrides
+      raw = request.cookies[Split::OVERRIDE_COOKIE_NAME]
+      return {} if raw.nil? || raw.empty?
+
+      overrides = JSON.parse(raw)
+      overrides.is_a?(Hash) ? overrides : {}
+    rescue JSON::ParserError
+      {}
+    end
+
+    def write_overrides(overrides)
+      if overrides.empty?
+        response.delete_cookie(Split::OVERRIDE_COOKIE_NAME, path: "/")
+      else
+        response.set_cookie(Split::OVERRIDE_COOKIE_NAME, { value: overrides.to_json, path: "/" })
+      end
+    end
+
     def url(*path_parts)
       [ request.env["SCRIPT_NAME"], path_parts ].join("/").squeeze("/")
     end

lib/split/dashboard/public/style.css

@@ -38,6 +38,9 @@ th, td { text-align: left; font-weight: normal; }
   --green-hover: light-dark(#267346, #45b075);
   --better: light-dark(#16a34a, #4ade80);
   --worse: light-dark(#dc2626, #f87171);
+  --warn-bg: light-dark(#fef3c7, #3a2f12);
+  --warn-border: light-dark(#fcd34d, #6b551c);
+  --warn-text: light-dark(#92400e, #fbbf24);
   --shadow-color: light-dark(rgba(0, 0, 0, 0.08), rgba(0, 0, 0, 0.4));
   --shadow: 0 1px 3px var(--shadow-color), 0 1px 2px var(--shadow-color);
   --radius: 8px;
@@ -203,6 +206,22 @@ a {
   font-weight: 400;
 }
 
+.experiment h2 .override {
+  margin-left: 6px;
+  padding: 2px 8px;
+  border-radius: 999px;
+  background: var(--warn-bg);
+  color: var(--warn-text);
+  font-size: 0.75em;
+  font-weight: 600;
+}
+
+.experiment table em.override-flag {
+  color: var(--warn-text);
+  font-style: normal;
+  font-weight: 600;
+}
+
 .experiment table em {
   font-style: italic;
   font-size: 0.9em;
@@ -250,9 +269,63 @@ a {
   color: var(--worse);
 }
 
+.overrides {
+  background: var(--warn-bg);
+  border: 1px solid var(--warn-border);
+  border-radius: var(--radius);
+  padding: 14px 18px;
+  margin-bottom: 20px;
+}
+
+.overrides-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 12px;
+}
+
+.overrides-header h2 {
+  margin: 0;
+  font-size: 1rem;
+  font-weight: 600;
+  color: var(--warn-text);
+}
+
+.overrides .overrides-intro {
+  margin: 8px 0 12px;
+  color: var(--text);
+  font-size: 0.85rem;
+  line-height: 1.5;
+}
+
+.overrides-list {
+  list-style: none;
+  margin: 0;
+  padding: 0;
+  display: flex;
+  flex-wrap: wrap;
+  gap: 8px;
+}
+
+.overrides-list li {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 6px 10px;
+  background: var(--surface);
+  border: 1px solid var(--warn-border);
+  border-radius: 6px;
+  font-size: 0.85rem;
+}
+
+.overrides-pair {
+  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
+}
+
 .experiment a.button,
 .experiment button,
 .experiment input[type="submit"],
+.overrides input[type="submit"],
 .dashboard-controls input[type="submit"],
 .dashboard-controls input[type="button"] {
   padding: 6px 14px;
@@ -273,19 +346,23 @@ a {
 .experiment button:hover,
 .experiment input[type="submit"]:hover,
 .experiment input[type="submit"]:focus,
+.overrides input[type="submit"]:hover,
+.overrides input[type="submit"]:focus,
 .dashboard-controls input[type="submit"]:hover,
 .dashboard-controls input[type="button"]:hover {
   background: var(--btn-bg-hover);
 }
 
 .experiment input[type="submit"].red,
-.experiment a.button.red {
+.experiment a.button.red,
+.overrides input[type="submit"].red {
   background: var(--red);
   color: #fff;
 }
 
 .experiment input[type="submit"].red:hover,
-.experiment a.button.red:hover {
+.experiment a.button.red:hover,
+.overrides input[type="submit"].red:hover {
   background: var(--red-hover);
 }
 

lib/split/dashboard/views/_experiment.erb

@@ -12,6 +12,9 @@
     <h2>
       Experiment: <%= experiment.name %>
       <% if experiment.version > 1 %><span class='version'>v<%= experiment.version %></span><% end %>
+      <% if (override = active_overrides[experiment.name]) %>
+        <span class='override' title='Your browser is pinned to this alternative'>Override:<%= h override.to_s %></span>
+      <% end %>
       <% unless goal.nil? %><span class='goal'>Goal:<%= goal %></span><% end %>
       <% metrics = @metrics.select {|metric| metric.experiments.include? experiment} %>
       <% unless metrics.empty? %>
@@ -52,6 +55,9 @@
           <% if alternative.control? %>
             <em>control</em>
           <% end %>
+          <% if active_overrides[experiment.name] == alternative.name %>
+            <em class="override-flag">forced for you</em>
+          <% end %>
           <form action="<%= url('force_alternative') + '?experiment=' + experiment.name %>" method='post'>
             <input type='hidden' name='alternative' value='<%= h alternative.name %>'>
             <input type="submit" value="Force for current user" class="green">

lib/split/dashboard/views/index.erb

@@ -1,3 +1,39 @@
+<% overrides = active_overrides %>
+<% unless overrides.empty? %>
+  <div class="overrides">
+    <div class="overrides-header">
+      <h2>Overrides active in this browser</h2>
+      <form action="<%= url "/clear_overrides" %>" method='post'>
+        <input type="submit" value="Clear all" class="red">
+      </form>
+    </div>
+
+    <p class="overrides-intro">
+      These pin <strong>your own</strong> visits to a fixed alternative. Other users are unaffected.
+      <% if Split.configuration.store_override %>
+        Your visits are still counted as participants.
+      <% else %>
+        Your visits are <strong>not counted</strong> as participants, so these experiments can read
+        zero below even though the page rendered an alternative for you.
+      <% end %>
+    </p>
+
+    <ul class="overrides-list">
+      <% overrides.sort.each do |experiment_name, alternative_name| %>
+        <li>
+          <span class="overrides-pair">
+            <%= h experiment_name %> &rarr; <strong><%= h alternative_name.to_s %></strong>
+          </span>
+          <form action="<%= url "/clear_override" %>" method='post'>
+            <input type='hidden' name='experiment' value='<%= h experiment_name %>'>
+            <input type="submit" value="Clear" class="red">
+          </form>
+        </li>
+      <% end %>
+    </ul>
+  </div>
+<% end %>
+
 <% if @experiment_names.any? %>
   <p class="intro">The list below contains all the registered experiments along with the number of test participants, completed and conversion rate currently in the system.</p>
 

lib/split/helper.rb

@@ -127,8 +127,8 @@ def override_alternative_by_params(experiment_name)
     def override_alternative_by_cookies(experiment_name)
       return unless request_present?
 
-      if request.cookies && request.cookies.key?("split_override")
-        experiments = JSON.parse(request.cookies["split_override"]) rescue {}
+      if request.cookies && request.cookies.key?(Split::OVERRIDE_COOKIE_NAME)
+        experiments = JSON.parse(request.cookies[Split::OVERRIDE_COOKIE_NAME]) rescue {}
         experiments[experiment_name]
       end
     end

spec/dashboard_helpers_spec.rb

@@ -40,4 +40,48 @@
       end
     end
   end
+
+  describe "active_overrides" do
+    let(:request) { double(cookies: cookies) }
+
+    context "with no override cookie" do
+      let(:cookies) { {} }
+
+      it "is empty" do
+        expect(active_overrides).to eq({})
+      end
+    end
+
+    context "with an empty override cookie" do
+      let(:cookies) { { "split_override" => "" } }
+
+      it "is empty" do
+        expect(active_overrides).to eq({})
+      end
+    end
+
+    context "with a valid override cookie" do
+      let(:cookies) { { "split_override" => '{"link_color":"blue"}' } }
+
+      it "returns the experiment to alternative mapping" do
+        expect(active_overrides).to eq("link_color" => "blue")
+      end
+    end
+
+    context "with a malformed override cookie" do
+      let(:cookies) { { "split_override" => "not json" } }
+
+      it "is empty rather than raising" do
+        expect(active_overrides).to eq({})
+      end
+    end
+
+    context "with a cookie holding JSON that is not an object" do
+      let(:cookies) { { "split_override" => '["link_color"]' } }
+
+      it "is empty" do
+        expect(active_overrides).to eq({})
+      end
+    end
+  end
 end