diff --git a/resources/celerity/map.php b/resources/celerity/map.php
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -393,6 +393,7 @@
     'rsrc/js/application/diffusion/behavior-audit-preview.js' => 'd835b03a',
     'rsrc/js/application/diffusion/behavior-commit-branches.js' => 'bdaf4d04',
     'rsrc/js/application/diffusion/behavior-commit-graph.js' => '5a0b1a64',
+    'rsrc/js/application/diffusion/behavior-diffusion-browse-file.js' => '054a0f0b',
     'rsrc/js/application/diffusion/behavior-jump-to.js' => '73d09eef',
     'rsrc/js/application/diffusion/behavior-load-blame.js' => '42126667',
     'rsrc/js/application/diffusion/behavior-locate-file.js' => '6d3e1947',
@@ -606,6 +607,7 @@
     'javelin-behavior-differential-populate' => '8694b1df',
     'javelin-behavior-differential-toggle-files' => 'ca3f91eb',
     'javelin-behavior-differential-user-select' => 'a8d8459d',
+    'javelin-behavior-diffusion-browse-file' => '054a0f0b',
     'javelin-behavior-diffusion-commit-branches' => 'bdaf4d04',
     'javelin-behavior-diffusion-commit-graph' => '5a0b1a64',
     'javelin-behavior-diffusion-jump-to' => '73d09eef',
@@ -918,6 +920,12 @@
       'javelin-util',
       'javelin-magical-init',
     ),
+    '054a0f0b' => array(
+      'javelin-behavior',
+      'javelin-dom',
+      'javelin-util',
+      'phabricator-tooltip',
+    ),
     '056da01b' => array(
       'aphront-typeahead-control-css',
       'phui-tag-view-css',
diff --git a/src/applications/diffusion/controller/DiffusionBrowseController.php b/src/applications/diffusion/controller/DiffusionBrowseController.php
--- a/src/applications/diffusion/controller/DiffusionBrowseController.php
+++ b/src/applications/diffusion/controller/DiffusionBrowseController.php
@@ -1187,6 +1187,19 @@
     $commit_links = $this->renderCommitLinks($blame_commits, $handles);
     $revision_links = $this->renderRevisionLinks($revisions, $handles);
 
+    if ($this->coverage) {
+      require_celerity_resource('differential-changeset-view-css');
+      Javelin::initBehavior(
+        'diffusion-browse-file',
+        array(
+          'labels' => array(
+            'cov-C' => pht('Covered'),
+            'cov-N' => pht('Not Covered'),
+            'cov-U' => pht('Not Executable'),
+          ),
+        ));
+    }
+
     $skip_text = pht('Skip Past This Commit');
     foreach ($display as $line_index => $line) {
       $row = array();
@@ -1304,7 +1317,6 @@
         ));
 
       if ($this->coverage) {
-        require_celerity_resource('differential-changeset-view-css');
         $cov_index = $line_index;
 
         if (isset($this->coverage[$cov_index])) {
diff --git a/webroot/rsrc/js/application/diffusion/behavior-diffusion-browse-file.js b/webroot/rsrc/js/application/diffusion/behavior-diffusion-browse-file.js
new file mode 100644
--- /dev/null
+++ b/webroot/rsrc/js/application/diffusion/behavior-diffusion-browse-file.js
@@ -0,0 +1,47 @@
+/**
+ * @provides javelin-behavior-diffusion-browse-file
+ * @requires javelin-behavior
+ *           javelin-dom
+ *           javelin-util
+ *           phabricator-tooltip
+ */
+
+JX.behavior('diffusion-browse-file', function(config, statics) {
+  if (statics.installed) {
+    return;
+  }
+  statics.installed = true;
+
+  var map = config.labels;
+
+  JX.Stratcom.listen(
+    ['mouseover', 'mouseout'],
+    ['phabricator-source', 'tag:td'],
+    function(e) {
+      var target = e.getTarget();
+
+      // NOTE: We're using raw classnames instead of sigils and metadata here
+      // because these elements are unusual: there are a lot of them on the
+      // page, and rendering all the extra metadata to do this in a normal way
+      // would be needlessly expensive. This is an unusual case.
+
+      if (!target.className.match(/cov-/)) {
+        return;
+      }
+
+      if (e.getType() == 'mouseout') {
+        JX.Tooltip.hide();
+        return;
+      }
+
+      for (var k in map) {
+        if (!target.className.match(k)) {
+          continue;
+        }
+
+        var label = map[k];
+        JX.Tooltip.show(target, 300, 'E', label);
+        break;
+      }
+    });
+});