diff --git a/resources/celerity/map.php b/resources/celerity/map.php
index 01dd75c901..1361bbd12c 100644
--- a/resources/celerity/map.php
+++ b/resources/celerity/map.php
@@ -78,7 +78,7 @@ return array(
     'rsrc/css/application/feed/feed.css' => 'ecd4ec57',
     'rsrc/css/application/files/global-drag-and-drop.css' => 'b556a948',
     'rsrc/css/application/flag/flag.css' => 'bba8f811',
-    'rsrc/css/application/harbormaster/harbormaster.css' => 'f491c9f4',
+    'rsrc/css/application/harbormaster/harbormaster.css' => 'fecac64f',
     'rsrc/css/application/herald/herald-test.css' => 'a52e323e',
     'rsrc/css/application/herald/herald.css' => 'cd8d0134',
     'rsrc/css/application/maniphest/report.css' => '9b9580b7',
@@ -416,6 +416,7 @@ return array(
     'rsrc/js/application/drydock/drydock-live-operation-status.js' => '901935ef',
     'rsrc/js/application/files/behavior-icon-composer.js' => '8499b6ab',
     'rsrc/js/application/files/behavior-launch-icon-composer.js' => '48086888',
+    'rsrc/js/application/harbormaster/behavior-harbormaster-log.js' => '0844f3c1',
     'rsrc/js/application/herald/HeraldRuleEditor.js' => 'dca75c0e',
     'rsrc/js/application/herald/PathTypeahead.js' => 'f7fc67ec',
     'rsrc/js/application/herald/herald-rule-editor.js' => '7ebaeed3',
@@ -578,7 +579,7 @@ return array(
     'font-fontawesome' => 'e838e088',
     'font-lato' => 'c7ccd872',
     'global-drag-and-drop-css' => 'b556a948',
-    'harbormaster-css' => 'f491c9f4',
+    'harbormaster-css' => 'fecac64f',
     'herald-css' => 'cd8d0134',
     'herald-rule-editor' => 'dca75c0e',
     'herald-test-css' => 'a52e323e',
@@ -635,6 +636,7 @@ return array(
     'javelin-behavior-event-all-day' => 'b41537c9',
     'javelin-behavior-fancy-datepicker' => 'ecf4e799',
     'javelin-behavior-global-drag-and-drop' => '960f6a39',
+    'javelin-behavior-harbormaster-log' => '0844f3c1',
     'javelin-behavior-herald-rule-editor' => '7ebaeed3',
     'javelin-behavior-high-security-warning' => 'a464fe03',
     'javelin-behavior-history-install' => '7ee2b591',
@@ -960,6 +962,9 @@ return array(
       'javelin-stratcom',
       'javelin-workflow',
     ),
+    '0844f3c1' => array(
+      'javelin-behavior',
+    ),
     '08f4ccc3' => array(
       'phui-oi-list-view-css',
     ),
diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index 01407ed67b..3a7ba1dbbc 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -1230,6 +1230,7 @@ phutil_register_library_map(array(
     'HarbormasterBuildLogDownloadController' => 'applications/harbormaster/controller/HarbormasterBuildLogDownloadController.php',
     'HarbormasterBuildLogPHIDType' => 'applications/harbormaster/phid/HarbormasterBuildLogPHIDType.php',
     'HarbormasterBuildLogQuery' => 'applications/harbormaster/query/HarbormasterBuildLogQuery.php',
+    'HarbormasterBuildLogRenderController' => 'applications/harbormaster/controller/HarbormasterBuildLogRenderController.php',
     'HarbormasterBuildLogTestCase' => 'applications/harbormaster/__tests__/HarbormasterBuildLogTestCase.php',
     'HarbormasterBuildLogView' => 'applications/harbormaster/view/HarbormasterBuildLogView.php',
     'HarbormasterBuildLogViewController' => 'applications/harbormaster/controller/HarbormasterBuildLogViewController.php',
@@ -6519,6 +6520,7 @@ phutil_register_library_map(array(
     'HarbormasterBuildLogDownloadController' => 'HarbormasterController',
     'HarbormasterBuildLogPHIDType' => 'PhabricatorPHIDType',
     'HarbormasterBuildLogQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
+    'HarbormasterBuildLogRenderController' => 'HarbormasterController',
     'HarbormasterBuildLogTestCase' => 'PhabricatorTestCase',
     'HarbormasterBuildLogView' => 'AphrontView',
     'HarbormasterBuildLogViewController' => 'HarbormasterController',
diff --git a/src/applications/harbormaster/application/PhabricatorHarbormasterApplication.php b/src/applications/harbormaster/application/PhabricatorHarbormasterApplication.php
index b4f62d8e22..103e6bce69 100644
--- a/src/applications/harbormaster/application/PhabricatorHarbormasterApplication.php
+++ b/src/applications/harbormaster/application/PhabricatorHarbormasterApplication.php
@@ -97,7 +97,10 @@ final class PhabricatorHarbormasterApplication extends PhabricatorApplication {
           'buildkite/' => 'HarbormasterBuildkiteHookController',
         ),
         'log/' => array(
-          'view/(?P<id>\d+)/' => 'HarbormasterBuildLogViewController',
+          'view/(?P<id>\d+)/(?:\$(?P<lines>\d+(?:-\d+)?))?'
+            => 'HarbormasterBuildLogViewController',
+          'render/(?P<id>\d+)/(?:\$(?P<lines>\d+(?:-\d+)?))?'
+            => 'HarbormasterBuildLogRenderController',
           'download/(?P<id>\d+)/' => 'HarbormasterBuildLogDownloadController',
         ),
       ),
diff --git a/src/applications/harbormaster/controller/HarbormasterBuildLogRenderController.php b/src/applications/harbormaster/controller/HarbormasterBuildLogRenderController.php
new file mode 100644
index 0000000000..a2322dc51d
--- /dev/null
+++ b/src/applications/harbormaster/controller/HarbormasterBuildLogRenderController.php
@@ -0,0 +1,562 @@
+<?php
+
+final class HarbormasterBuildLogRenderController
+  extends HarbormasterController {
+
+  public function handleRequest(AphrontRequest $request) {
+    $viewer = $this->getViewer();
+
+    $id = $request->getURIData('id');
+
+    $log = id(new HarbormasterBuildLogQuery())
+      ->setViewer($viewer)
+      ->withIDs(array($id))
+      ->executeOne();
+    if (!$log) {
+      return new Aphront404Response();
+    }
+
+    $log_size = $this->getTotalByteLength($log);
+
+    $head_lines = $request->getInt('head');
+    if ($head_lines === null) {
+      $head_lines = 8;
+    }
+    $head_lines = min($head_lines, 100);
+    $head_lines = max($head_lines, 0);
+
+    $tail_lines = $request->getInt('tail');
+    if ($tail_lines === null) {
+      $tail_lines = 16;
+    }
+    $tail_lines = min($tail_lines, 100);
+    $tail_lines = max($tail_lines, 0);
+
+    $head_offset = $request->getInt('headOffset');
+    if ($head_offset === null) {
+      $head_offset = 0;
+    }
+
+    $tail_offset = $request->getInt('tailOffset');
+    if ($tail_offset === null) {
+      $tail_offset = $log_size;
+    }
+
+    // Figure out which ranges we're actually going to read. We'll read either
+    // one range (either just at the head, or just at the tail) or two ranges
+    // (one at the head and one at the tail).
+
+    // This gets a little bit tricky because: the ranges may overlap; we just
+    // want to do one big read if there is only a little bit of text left
+    // between the ranges; we may not know where the tail range ends; and we
+    // can only read forward from line map markers, not from any arbitrary
+    // position in the file.
+
+    $bytes_per_line = 140;
+    $body_lines = 8;
+
+    $views = array();
+    if ($head_lines > 0) {
+      $views[] = array(
+        'offset' => $head_offset,
+        'lines' => $head_lines,
+        'direction' => 1,
+      );
+    }
+
+    if ($tail_lines > 0) {
+      $views[] = array(
+        'offset' => $tail_offset,
+        'lines' => $tail_lines,
+        'direction' => -1,
+      );
+    }
+
+    $reads = $views;
+    foreach ($reads as $key => $read) {
+      $offset = $read['offset'];
+
+      $lines = $read['lines'];
+
+      $read_length = 0;
+      $read_length += ($lines * $bytes_per_line);
+      $read_length += ($body_lines * $bytes_per_line);
+
+      $direction = $read['direction'];
+      if ($direction < 0) {
+        $offset -= $read_length;
+        if ($offset < 0) {
+          $offset = 0;
+          $read_length = $log_size;
+        }
+      }
+
+      $position = $log->getReadPosition($offset);
+      list($position_offset, $position_line) = $position;
+      $read_length += ($offset - $position_offset);
+
+      $reads[$key]['fetchOffset'] = $position_offset;
+      $reads[$key]['fetchLength'] = $read_length;
+      $reads[$key]['fetchLine'] = $position_line;
+    }
+
+    $reads = $this->mergeOverlappingReads($reads);
+
+    foreach ($reads as $key => $read) {
+      $data = $log->loadData($read['fetchOffset'], $read['fetchLength']);
+
+      $offset = $read['fetchOffset'];
+      $line = $read['fetchLine'];
+      $lines = $this->getLines($data);
+      $line_data = array();
+      foreach ($lines as $line_text) {
+        $length = strlen($line_text);
+        $line_data[] = array(
+          'offset' => $offset,
+          'length' => $length,
+          'line' => $line,
+          'data' => $line_text,
+        );
+        $line += 1;
+        $offset += $length;
+      }
+
+      $reads[$key]['data'] = $data;
+      $reads[$key]['lines'] = $line_data;
+    }
+
+    foreach ($views as $view_key => $view) {
+      $anchor_byte = $view['offset'];
+
+      $data_key = null;
+      foreach ($reads as $read_key => $read) {
+        $s = $read['fetchOffset'];
+        $e = $s + $read['fetchLength'];
+
+        if (($s <= $anchor_byte) && ($e >= $anchor_byte)) {
+          $data_key = $read_key;
+          break;
+        }
+      }
+
+      if ($data_key === null) {
+        throw new Exception(
+          pht('Unable to find fetch!'));
+      }
+
+      $anchor_key = null;
+      foreach ($reads[$data_key]['lines'] as $line_key => $line) {
+        $s = $line['offset'];
+        $e = $s + $line['length'];
+        if (($s <= $anchor_byte) && ($e >= $anchor_byte)) {
+          $anchor_key = $line_key;
+          break;
+        }
+      }
+
+      if ($anchor_key === null) {
+        throw new Exception(
+          pht(
+            'Unable to find lines.'));
+      }
+
+      if ($direction > 0) {
+        $slice_offset = $line_key;
+      } else {
+        $slice_offset = max(0, $line_key - ($view['lines'] - 1));
+      }
+      $slice_length = $view['lines'];
+
+      $views[$view_key] += array(
+        'sliceKey' => $data_key,
+        'sliceOffset' => $slice_offset,
+        'sliceLength' => $slice_length,
+      );
+    }
+
+    foreach ($views as $view_key => $view) {
+      $slice_key = $view['sliceKey'];
+      $lines = array_slice(
+        $reads[$slice_key]['lines'],
+        $view['sliceOffset'],
+        $view['sliceLength']);
+
+      $data_offset = null;
+      $data_length = null;
+      foreach ($lines as $line) {
+        if ($data_offset === null) {
+          $data_offset = $line['offset'];
+        }
+        $data_length += $line['length'];
+      }
+
+      // If the view cursor starts in the middle of a line, we're going to
+      // strip part of the line.
+      $direction = $view['direction'];
+      if ($direction > 0) {
+        $view_offset = $view['offset'];
+        $view_length = $data_length;
+        if ($data_offset < $view_offset) {
+          $trim = ($view_offset - $data_offset);
+          $view_length -= $trim;
+        }
+      } else {
+        $view_offset = $data_offset;
+        $view_length = $data_length;
+        if ($data_offset + $data_length > $view['offset']) {
+          $view_length -= (($data_offset + $data_length) - $view['offset']);
+        }
+      }
+
+      $views[$view_key] += array(
+        'viewOffset' => $view_offset,
+        'viewLength' => $view_length,
+      );
+    }
+
+    $views = $this->mergeOverlappingViews($views);
+
+    foreach ($views as $view_key => $view) {
+      $slice_key = $view['sliceKey'];
+      $lines = array_slice(
+        $reads[$slice_key]['lines'],
+        $view['sliceOffset'],
+        $view['sliceLength']);
+
+      $view_offset = $view['viewOffset'];
+      foreach ($lines as $line_key => $line) {
+        $line_offset = $line['offset'];
+
+        if ($line_offset >= $view_offset) {
+          break;
+        }
+
+        $trim = ($view_offset - $line_offset);
+        $line_data = substr($line['data'], $trim);
+        if (!strlen($line_data)) {
+          unset($lines[$line_key]);
+          continue;
+        }
+
+        $lines[$line_key]['data'] = $line_data;
+        $lines[$line_key]['length'] = strlen($line_data);
+        $lines[$line_key]['offset'] += $trim;
+        break;
+      }
+
+      $view_end = $view['viewOffset'] + $view['viewLength'];
+      foreach ($lines as $line_key => $line) {
+        $line_end = $line['offset'] + $line['length'];
+        if ($line_end <= $view_end) {
+          break;
+        }
+
+        $trim = ($line_end - $view_end);
+        $line_data = substr($line['data'], -$trim);
+        if (!strlen($line_data)) {
+          unset($lines[$line_key]);
+          continue;
+        }
+
+        $lines[$line_key]['data'] = $line_data;
+        $lines[$line_key]['length'] = strlen($line_data);
+      }
+
+      $views[$view_key]['viewData'] = $lines;
+    }
+
+    $spacer = null;
+    $render = array();
+    foreach ($views as $view) {
+      if ($spacer) {
+        $spacer['tail'] = $view['viewOffset'];
+        $render[] = $spacer;
+      }
+
+      $render[] = $view;
+
+      $spacer = array(
+        'spacer' => true,
+        'head' => ($view['viewOffset'] + $view['viewLength']),
+      );
+    }
+
+    $uri = $log->getURI();
+    $highlight_range = $request->getURIData('lines');
+
+    $rows = array();
+    foreach ($render as $range) {
+      if (isset($range['spacer'])) {
+        $rows[] = phutil_tag(
+          'tr',
+          array(),
+          array(
+            phutil_tag(
+              'th',
+              array(),
+              null),
+            phutil_tag(
+              'td',
+              array(),
+              array(
+                javelin_tag(
+                  'a',
+                  array(
+                    'sigil' => 'harbormaster-log-expand',
+                    'meta' => array(
+                      'headOffset' => $range['head'],
+                      'tailOffset' => $range['tail'],
+                      'head' => 4,
+                    ),
+                  ),
+                  'Show Up ^^^^'),
+                '... '.($range['tail'] - $range['head']).' bytes ...',
+                javelin_tag(
+                  'a',
+                  array(
+                    'sigil' => 'harbormaster-log-expand',
+                    'meta' => array(
+                      'headOffset' => $range['head'],
+                      'tailOffset' => $range['tail'],
+                      'tail' => 4,
+                    ),
+                  ),
+                  'Show Down VVVV'),
+              )),
+          ));
+        continue;
+      }
+
+      $lines = $range['viewData'];
+      foreach ($lines as $line) {
+        $display_line = ($line['line'] + 1);
+        $display_text = ($line['data']);
+
+        $display_line = phutil_tag(
+          'a',
+          array(
+            'href' => $uri.'$'.$display_line,
+          ),
+          $display_line);
+
+        $line_cell = phutil_tag('th', array(), $display_line);
+        $text_cell = phutil_tag('td', array(), $display_text);
+
+        $rows[] = phutil_tag(
+          'tr',
+          array(),
+          array(
+            $line_cell,
+            $text_cell,
+          ));
+      }
+    }
+
+    $table = phutil_tag(
+      'table',
+      array(
+        'class' => 'harbormaster-log-table PhabricatorMonospaced',
+      ),
+      $rows);
+
+    // When this is a normal AJAX request, return the rendered log fragment
+    // in an AJAX payload.
+    if ($request->isAjax()) {
+      return id(new AphrontAjaxResponse())
+        ->setContent(
+          array(
+            'markup' => hsprintf('%s', $table),
+          ));
+    }
+
+    // If the page is being accessed as a standalone page, present a
+    // readable version of the fragment for debugging.
+
+    require_celerity_resource('harbormaster-css');
+
+    $header = pht('Standalone Log Fragment');
+
+    $render_view = id(new PHUIObjectBoxView())
+      ->setBackground(PHUIObjectBoxView::BLUE_PROPERTY)
+      ->setHeaderText($header)
+      ->appendChild($table);
+
+    $page_view = id(new PHUITwoColumnView())
+      ->setFooter($render_view);
+
+    $crumbs = $this->buildApplicationCrumbs()
+      ->addTextCrumb(pht('Build Log %d', $log->getID()), $log->getURI())
+      ->addTextCrumb(pht('Fragment'))
+      ->setBorder(true);
+
+    return $this->newPage()
+      ->setTitle(
+        array(
+          pht('Build Log %d', $log->getID()),
+          pht('Standalone Fragment'),
+        ))
+      ->setCrumbs($crumbs)
+      ->appendChild($page_view);
+  }
+
+  private function getTotalByteLength(HarbormasterBuildLog $log) {
+    $total_bytes = $log->getByteLength();
+    if ($total_bytes) {
+      return (int)$total_bytes;
+    }
+
+    // TODO: Remove this after enough time has passed for installs to run
+    // log rebuilds or decide they don't care about older logs.
+
+    // Older logs don't have this data denormalized onto the log record unless
+    // an administrator has run `bin/harbormaster rebuild-log --all` or
+    // similar. Try to figure it out by summing up the size of each chunk.
+
+    // Note that the log may also be legitimately empty and have actual size
+    // zero.
+    $chunk = new HarbormasterBuildLogChunk();
+    $conn = $chunk->establishConnection('r');
+
+    $row = queryfx_one(
+      $conn,
+      'SELECT SUM(size) total FROM %T WHERE logID = %d',
+      $chunk->getTableName(),
+      $log->getID());
+
+    return (int)$row['total'];
+  }
+
+  private function getLines($data) {
+    $parts = preg_split("/(\r\n|\r|\n)/", $data, 0, PREG_SPLIT_DELIM_CAPTURE);
+
+    if (last($parts) === '') {
+      array_pop($parts);
+    }
+
+    $lines = array();
+    for ($ii = 0; $ii < count($parts); $ii += 2) {
+      $line = $parts[$ii];
+      if (isset($parts[$ii + 1])) {
+        $line .= $parts[$ii + 1];
+      }
+      $lines[] = $line;
+    }
+
+    return $lines;
+  }
+
+
+  private function mergeOverlappingReads(array $reads) {
+    // Find planned reads which will overlap and merge them into a single
+    // larger read.
+
+    $uk = array_keys($reads);
+    $vk = array_keys($reads);
+
+    foreach ($uk as $ukey) {
+      foreach ($vk as $vkey) {
+        // Don't merge a range into itself, even though they do technically
+        // overlap.
+        if ($ukey === $vkey) {
+          continue;
+        }
+
+        $uread = idx($reads, $ukey);
+        if ($uread === null) {
+          continue;
+        }
+
+        $vread = idx($reads, $vkey);
+        if ($vread === null) {
+          continue;
+        }
+
+        $us = $uread['fetchOffset'];
+        $ue = $us + $uread['fetchLength'];
+
+        $vs = $vread['fetchOffset'];
+        $ve = $vs + $vread['fetchLength'];
+
+        if (($vs > $ue) || ($ve < $us)) {
+          continue;
+        }
+
+        $min = min($us, $vs);
+        $max = max($ue, $ve);
+
+        $reads[$ukey]['fetchOffset'] = $min;
+        $reads[$ukey]['fetchLength'] = ($max - $min);
+        $reads[$ukey]['fetchLine'] = min(
+          $uread['fetchLine'],
+          $vread['fetchLine']);
+
+        unset($reads[$vkey]);
+      }
+    }
+
+    return $reads;
+  }
+
+  private function mergeOverlappingViews(array $views) {
+    $uk = array_keys($views);
+    $vk = array_keys($views);
+
+    $body_lines = 8;
+    $body_bytes = ($body_lines * 140);
+
+    foreach ($uk as $ukey) {
+      foreach ($vk as $vkey) {
+        if ($ukey === $vkey) {
+          continue;
+        }
+
+        $uview = idx($views, $ukey);
+        if ($uview === null) {
+          continue;
+        }
+
+        $vview = idx($views, $vkey);
+        if ($vview === null) {
+          continue;
+        }
+
+        // If these views don't use the same line data, don't try to
+        // merge them.
+        if ($uview['sliceKey'] != $vview['sliceKey']) {
+          continue;
+        }
+
+        // If these views are overlapping or separated by only a few bytes,
+        // merge them into a single view.
+        $us = $uview['viewOffset'];
+        $ue = $us + $uview['viewLength'];
+
+        $vs = $vview['viewOffset'];
+        $ve = $vs + $vview['viewLength'];
+
+        $uss = $uview['sliceOffset'];
+        $use = $uss + $uview['sliceLength'];
+
+        $vss = $vview['sliceOffset'];
+        $vse = $vss + $vview['sliceLength'];
+
+        if ($ue <= $vs) {
+          if (($ue + $body_bytes) >= $vs) {
+            if (($use + $body_lines) >= $vss) {
+              $views[$ukey] = array(
+                'sliceLength' => ($vse - $uss),
+                'viewLength' => ($ve - $us),
+              ) + $views[$ukey];
+
+              unset($views[$vkey]);
+              continue;
+            }
+          }
+        }
+      }
+    }
+
+    return $views;
+  }
+
+}
diff --git a/src/applications/harbormaster/controller/HarbormasterBuildLogViewController.php b/src/applications/harbormaster/controller/HarbormasterBuildLogViewController.php
index 084c48d1f1..41f2aef8e5 100644
--- a/src/applications/harbormaster/controller/HarbormasterBuildLogViewController.php
+++ b/src/applications/harbormaster/controller/HarbormasterBuildLogViewController.php
@@ -4,8 +4,7 @@ final class HarbormasterBuildLogViewController
   extends HarbormasterController {
 
   public function handleRequest(AphrontRequest $request) {
-    $request = $this->getRequest();
-    $viewer = $request->getUser();
+    $viewer = $this->getViewer();
 
     $id = $request->getURIData('id');
 
@@ -21,7 +20,8 @@ final class HarbormasterBuildLogViewController
 
     $log_view = id(new HarbormasterBuildLogView())
       ->setViewer($viewer)
-      ->setBuildLog($log);
+      ->setBuildLog($log)
+      ->setHighlightedLineRange($request->getURIData('lines'));
 
     $crumbs = $this->buildApplicationCrumbs()
       ->addTextCrumb(pht('Build Logs'))
diff --git a/src/applications/harbormaster/storage/build/HarbormasterBuildLog.php b/src/applications/harbormaster/storage/build/HarbormasterBuildLog.php
index 9b983f0733..64934bbea8 100644
--- a/src/applications/harbormaster/storage/build/HarbormasterBuildLog.php
+++ b/src/applications/harbormaster/storage/build/HarbormasterBuildLog.php
@@ -129,6 +129,30 @@ final class HarbormasterBuildLog
       $this->getID());
   }
 
+  public function loadData($offset, $length) {
+    return substr($this->getLogText(), $offset, $length);
+  }
+
+  public function getReadPosition($read_offset) {
+    $position = array(0, 0);
+
+    $map = $this->getLineMap();
+    if (!$map) {
+      throw new Exception(pht('No line map.'));
+    }
+
+    list($map) = $map;
+    foreach ($map as $marker) {
+      list($offset, $count) = $marker;
+      if ($offset > $read_offset) {
+        break;
+      }
+      $position = $marker;
+    }
+
+    return $position;
+  }
+
   public function getLogText() {
     // TODO: Remove this method since it won't scale for big logs.
 
@@ -148,6 +172,15 @@ final class HarbormasterBuildLog
     return "/harbormaster/log/view/{$id}/";
   }
 
+  public function getRenderURI($lines) {
+    if (strlen($lines)) {
+      $lines = '$'.$lines;
+    }
+
+    $id = $this->getID();
+    return "/harbormaster/log/render/{$id}/{$lines}";
+  }
+
 
 /* -(  Chunks  )------------------------------------------------------------- */
 
diff --git a/src/applications/harbormaster/view/HarbormasterBuildLogView.php b/src/applications/harbormaster/view/HarbormasterBuildLogView.php
index 7543524285..81705f3f49 100644
--- a/src/applications/harbormaster/view/HarbormasterBuildLogView.php
+++ b/src/applications/harbormaster/view/HarbormasterBuildLogView.php
@@ -3,6 +3,7 @@
 final class HarbormasterBuildLogView extends AphrontView {
 
   private $log;
+  private $highlightedLineRange;
 
   public function setBuildLog(HarbormasterBuildLog $log) {
     $this->log = $log;
@@ -13,6 +14,15 @@ final class HarbormasterBuildLogView extends AphrontView {
     return $this->log;
   }
 
+  public function setHighlightedLineRange($range) {
+    $this->highlightedLineRange = $range;
+    return $this;
+  }
+
+  public function getHighlightedLineRange() {
+    return $this->highlightedLineRange;
+  }
+
   public function render() {
     $viewer = $this->getViewer();
     $log = $this->getBuildLog();
@@ -34,10 +44,28 @@ final class HarbormasterBuildLogView extends AphrontView {
 
     $header->addActionLink($download_button);
 
+    $content_id = celerity_generate_unique_node_id();
+    $content_div = javelin_tag(
+      'div',
+      array(
+        'id' => $content_id,
+        'class' => 'harbormaster-log-view-loading',
+      ),
+      pht('Loading...'));
+
+    require_celerity_resource('harbormaster-css');
+
+    Javelin::initBehavior(
+      'harbormaster-log',
+      array(
+        'contentNodeID' => $content_id,
+        'renderURI' => $log->getRenderURI($this->getHighlightedLineRange()),
+      ));
+
     $box_view = id(new PHUIObjectBoxView())
       ->setBackground(PHUIObjectBoxView::BLUE_PROPERTY)
       ->setHeader($header)
-      ->appendChild('...');
+      ->appendChild($content_div);
 
     return $box_view;
   }
diff --git a/webroot/rsrc/css/application/harbormaster/harbormaster.css b/webroot/rsrc/css/application/harbormaster/harbormaster.css
index 4bfd2d6cbe..f55139ade0 100644
--- a/webroot/rsrc/css/application/harbormaster/harbormaster.css
+++ b/webroot/rsrc/css/application/harbormaster/harbormaster.css
@@ -30,3 +30,41 @@
   text-overflow: ellipsis;
   color: {$lightgreytext};
 }
+
+.harbormaster-log-view-loading {
+  padding: 8px;
+  text-align: center;
+  color: {$lightgreytext};
+}
+
+.harbormaster-log-table th {
+  background-color: {$paste.highlight};
+  border-right: 1px solid {$paste.border};
+
+  -moz-user-select: -moz-none;
+  -khtml-user-select: none;
+  -webkit-user-select: none;
+  -ms-user-select: none;
+  user-select: none;
+}
+
+.harbormaster-log-table th a {
+  display: block;
+  color: {$darkbluetext};
+  text-align: right;
+  padding: 2px 6px 1px 12px;
+}
+
+.harbormaster-log-table th a:hover {
+  background: {$paste.border};
+}
+
+.harbormaster-log-table td {
+  white-space: pre-wrap;
+  padding: 2px 8px 1px;
+  width: 100%;
+}
+
+.harbormaster-log-table tr.harbormaster-log-highlighted td {
+  background: {$paste.highlight};
+}
diff --git a/webroot/rsrc/js/application/harbormaster/behavior-harbormaster-log.js b/webroot/rsrc/js/application/harbormaster/behavior-harbormaster-log.js
new file mode 100644
index 0000000000..d011233afd
--- /dev/null
+++ b/webroot/rsrc/js/application/harbormaster/behavior-harbormaster-log.js
@@ -0,0 +1,43 @@
+/**
+ * @provides javelin-behavior-harbormaster-log
+ * @requires javelin-behavior
+ */
+
+JX.behavior('harbormaster-log', function(config) {
+  var contentNode = JX.$(config.contentNodeID);
+
+  JX.DOM.listen(contentNode, 'click', 'harbormaster-log-expand', function(e) {
+    if (!e.isNormalClick()) {
+      return;
+    }
+
+    e.kill();
+
+    var row = e.getNode('tag:tr');
+    var data = e.getNodeData('harbormaster-log-expand');
+
+    var uri = new JX.URI(config.renderURI)
+      .addQueryParams(data);
+
+    var request = new JX.Request(uri, function(r) {
+      var result = JX.$H(r.markup).getNode();
+      var rows = JX.DOM.scry(result, 'tr');
+
+      JX.DOM.replace(row, rows);
+    });
+
+    request.send();
+  });
+
+  function onresponse(r) {
+    JX.DOM.alterClass(contentNode, 'harbormaster-log-view-loading', false);
+
+    JX.DOM.setContent(contentNode, JX.$H(r.markup));
+  }
+
+  var uri = new JX.URI(config.renderURI);
+
+  new JX.Request(uri, onresponse)
+    .send();
+
+});