diff --git a/scripts/utils/prosediff.php b/scripts/utils/prosediff.php
deleted file mode 100755
--- a/scripts/utils/prosediff.php
+++ /dev/null
@@ -1,50 +0,0 @@
-#!/usr/bin/env php
-<?php
-
-require_once dirname(__FILE__).'/../__init_script__.php';
-
-$args = new PhutilArgumentParser($argv);
-$args->setTagline(pht('show prose differences'));
-$args->setSynopsis(<<<EOHELP
-**prosediff.php** __old__ __new__ [__options__]
-    Diff two prose files.
-
-EOHELP
-);
-
-$args->parseStandardArguments();
-$args->parse(
-  array(
-    array(
-      'name'      => 'files',
-      'wildcard'  => true,
-    ),
-  ));
-
-$files = $args->getArg('files');
-if (count($files) !== 2) {
-  $args->printHelpAndExit();
-}
-$old_file = head($files);
-$new_file = last($files);
-
-$old_data = Filesystem::readFile($old_file);
-$new_data = Filesystem::readFile($new_file);
-
-$engine = new PhutilProseDifferenceEngine();
-
-$prose_diff = $engine->getDiff($old_data, $new_data);
-
-foreach ($prose_diff->getParts() as $part) {
-  switch ($part['type']) {
-    case '-':
-      echo tsprintf('<bg:red>%B</bg>', $part['text']);
-      break;
-    case '+':
-      echo tsprintf('<bg:green>%B</bg>', $part['text']);
-      break;
-    case '=':
-      echo tsprintf('%B', $part['text']);
-      break;
-  }
-}
diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -297,9 +297,6 @@
     'PhutilProcessRef' => 'filesystem/PhutilProcessRef.php',
     'PhutilProcessRefTestCase' => 'filesystem/__tests__/PhutilProcessRefTestCase.php',
     'PhutilProgressSink' => 'progress/PhutilProgressSink.php',
-    'PhutilProseDiff' => 'utils/PhutilProseDiff.php',
-    'PhutilProseDiffTestCase' => 'utils/__tests__/PhutilProseDiffTestCase.php',
-    'PhutilProseDifferenceEngine' => 'utils/PhutilProseDifferenceEngine.php',
     'PhutilProtocolChannel' => 'channel/PhutilProtocolChannel.php',
     'PhutilProxyException' => 'error/PhutilProxyException.php',
     'PhutilProxyIterator' => 'utils/PhutilProxyIterator.php',
@@ -841,9 +838,6 @@
     'PhutilProcessRef' => 'Phobject',
     'PhutilProcessRefTestCase' => 'PhutilTestCase',
     'PhutilProgressSink' => 'Phobject',
-    'PhutilProseDiff' => 'Phobject',
-    'PhutilProseDiffTestCase' => 'PhutilTestCase',
-    'PhutilProseDifferenceEngine' => 'Phobject',
     'PhutilProtocolChannel' => 'PhutilChannelChannel',
     'PhutilProxyException' => 'Exception',
     'PhutilProxyIterator' => array(
diff --git a/src/utils/PhutilProseDiff.php b/src/utils/PhutilProseDiff.php
deleted file mode 100644
--- a/src/utils/PhutilProseDiff.php
+++ /dev/null
@@ -1,292 +0,0 @@
-<?php
-
-final class PhutilProseDiff extends Phobject {
-
-  private $parts = array();
-
-  public function addPart($type, $text) {
-    $this->parts[] = array(
-      'type' => $type,
-      'text' => $text,
-    );
-    return $this;
-  }
-
-  public function getParts() {
-    return $this->parts;
-  }
-
-  /**
-   * Get diff parts, but replace large blocks of unchanged text with "."
-   * parts representing missing context.
-   */
-  public function getSummaryParts() {
-    $parts = $this->getParts();
-
-    $head_key = head_key($parts);
-    $last_key = last_key($parts);
-
-    $results = array();
-    foreach ($parts as $key => $part) {
-      $is_head = ($key == $head_key);
-      $is_last = ($key == $last_key);
-
-      switch ($part['type']) {
-        case '=':
-          $pieces = $this->splitTextForSummary($part['text']);
-
-          if ($is_head || $is_last) {
-            $need = 2;
-          } else {
-            $need = 3;
-          }
-
-          // We don't have enough pieces to omit anything, so just continue.
-          if (count($pieces) < $need) {
-            $results[] = $part;
-            break;
-          }
-
-          if (!$is_head) {
-            $results[] = array(
-              'type' => '=',
-              'text' => head($pieces),
-            );
-          }
-
-          $results[] = array(
-            'type' => '.',
-            'text' => null,
-          );
-
-          if (!$is_last) {
-            $results[] = array(
-              'type' => '=',
-              'text' => last($pieces),
-            );
-          }
-          break;
-        default:
-          $results[] = $part;
-          break;
-      }
-    }
-
-    return $results;
-  }
-
-
-  public function reorderParts() {
-    // Reorder sequences of removed and added sections to put all the "-"
-    // parts together first, then all the "+" parts together. This produces
-    // a more human-readable result than intermingling them.
-
-    $o_run = array();
-    $n_run = array();
-    $result = array();
-    foreach ($this->parts as $part) {
-      $type = $part['type'];
-      switch ($type) {
-        case '-':
-          $o_run[] = $part;
-          break;
-        case '+':
-          $n_run[] = $part;
-          break;
-        default:
-          if ($o_run || $n_run) {
-            foreach ($this->combineRuns($o_run, $n_run) as $merged_part) {
-              $result[] = $merged_part;
-            }
-            $o_run = array();
-            $n_run = array();
-          }
-          $result[] = $part;
-          break;
-      }
-    }
-
-    if ($o_run || $n_run) {
-      foreach ($this->combineRuns($o_run, $n_run) as $part) {
-        $result[] = $part;
-      }
-    }
-
-    // Now, combine consecuitive runs of the same type of change (like a
-    // series of "-" parts) into a single run.
-    $combined = array();
-
-    $last = null;
-    $last_text = null;
-    foreach ($result as $part) {
-      $type = $part['type'];
-
-      if ($last !== $type) {
-        if ($last !== null) {
-          $combined[] = array(
-            'type' => $last,
-            'text' => $last_text,
-          );
-        }
-        $last_text = null;
-        $last = $type;
-      }
-
-      $last_text .= $part['text'];
-    }
-
-    if ($last_text !== null) {
-      $combined[] = array(
-        'type' => $last,
-        'text' => $last_text,
-      );
-    }
-
-    $this->parts = $combined;
-
-    return $this;
-  }
-
-  private function combineRuns($o_run, $n_run) {
-    $o_merge = $this->mergeParts($o_run);
-    $n_merge = $this->mergeParts($n_run);
-
-    // When removed and added blocks share a prefix or suffix, we sometimes
-    // want to count it as unchanged (for example, if it is whitespace) but
-    // sometimes want to count it as changed (for example, if it is a word
-    // suffix like "ing"). Find common prefixes and suffixes of these layout
-    // characters and emit them as "=" (unchanged) blocks.
-
-    $layout_characters = array(
-      ' ' => true,
-      "\n" => true,
-      '.' => true,
-      '!' => true,
-      ',' => true,
-      '?' => true,
-      ']' => true,
-      '[' => true,
-      '(' => true,
-      ')' => true,
-      '<' => true,
-      '>' => true,
-    );
-
-    $o_text = $o_merge['text'];
-    $n_text = $n_merge['text'];
-    $o_len = strlen($o_text);
-    $n_len = strlen($n_text);
-    $min_len = min($o_len, $n_len);
-
-    $prefix_len = 0;
-    for ($pos = 0; $pos < $min_len; $pos++) {
-      $o = $o_text[$pos];
-      $n = $n_text[$pos];
-      if ($o !== $n) {
-        break;
-      }
-      if (empty($layout_characters[$o])) {
-        break;
-      }
-      $prefix_len++;
-    }
-
-    $suffix_len = 0;
-    for ($pos = 0; $pos < ($min_len - $prefix_len); $pos++) {
-      $o = $o_text[$o_len - ($pos + 1)];
-      $n = $n_text[$n_len - ($pos + 1)];
-      if ($o !== $n) {
-        break;
-      }
-      if (empty($layout_characters[$o])) {
-        break;
-      }
-      $suffix_len++;
-    }
-
-    $results = array();
-
-    if ($prefix_len) {
-      $results[] = array(
-        'type' => '=',
-        'text' => substr($o_text, 0, $prefix_len),
-      );
-    }
-
-    if ($prefix_len < $o_len) {
-      $results[] = array(
-        'type' => '-',
-        'text' => substr(
-          $o_text,
-          $prefix_len,
-          $o_len - $prefix_len - $suffix_len),
-      );
-    }
-
-    if ($prefix_len < $n_len) {
-      $results[] = array(
-        'type' => '+',
-        'text' => substr(
-          $n_text,
-          $prefix_len,
-          $n_len - $prefix_len - $suffix_len),
-      );
-    }
-
-    if ($suffix_len) {
-      $results[] = array(
-        'type' => '=',
-        'text' => substr($o_text, -$suffix_len),
-      );
-    }
-
-    return $results;
-  }
-
-  private function mergeParts(array $parts) {
-    $text = '';
-    $type = null;
-    foreach ($parts as $part) {
-      $part_type = $part['type'];
-      if ($type === null) {
-        $type = $part_type;
-      }
-      if ($type !== $part_type) {
-        throw new Exception(pht('Can not merge parts of dissimilar types!'));
-      }
-      $text .= $part['text'];
-    }
-
-    return array(
-      'type' => $type,
-      'text' => $text,
-    );
-  }
-
-  private function splitTextForSummary($text) {
-    $matches = null;
-
-    $ok = preg_match('/^(\n*[^\n]+)\n/', $text, $matches);
-    if (!$ok) {
-      return array($text);
-    }
-
-    $head = $matches[1];
-    $text = substr($text, strlen($head));
-
-    $ok = preg_match('/\n([^\n]+\n*)\z/', $text, $matches);
-    if (!$ok) {
-      return array($text);
-    }
-
-    $last = $matches[1];
-    $text = substr($text, 0, -strlen($last));
-
-    if (!strlen(trim($text))) {
-      return array($head, $last);
-    } else {
-      return array($head, $text, $last);
-    }
-  }
-
-}
diff --git a/src/utils/PhutilProseDifferenceEngine.php b/src/utils/PhutilProseDifferenceEngine.php
deleted file mode 100644
--- a/src/utils/PhutilProseDifferenceEngine.php
+++ /dev/null
@@ -1,209 +0,0 @@
-<?php
-
-final class PhutilProseDifferenceEngine extends Phobject {
-
-  public function getDiff($u, $v) {
-    return $this->buildDiff($u, $v, 0);
-  }
-
-  private function buildDiff($u, $v, $level) {
-    $u_parts = $this->splitCorpus($u, $level);
-    $v_parts = $this->splitCorpus($v, $level);
-
-    $matrix = id(new PhutilEditDistanceMatrix())
-      ->setMaximumLength(128)
-      ->setSequences($u_parts, $v_parts)
-      ->setComputeString(true);
-
-    // For word-level and character-level changes, smooth the output string
-    // to reduce the choppiness of the diff.
-    if ($level > 1) {
-      $matrix->setApplySmoothing(PhutilEditDistanceMatrix::SMOOTHING_FULL);
-    }
-
-    $u_pos = 0;
-    $v_pos = 0;
-
-    $edits = $matrix->getEditString();
-    $edits_length = strlen($edits);
-
-    $diff = new PhutilProseDiff();
-    for ($ii = 0; $ii < $edits_length; $ii++) {
-      $c = $edits[$ii];
-      if ($c == 's') {
-        $diff->addPart('=', $u_parts[$u_pos]);
-        $u_pos++;
-        $v_pos++;
-      } else if ($c == 'd') {
-        $diff->addPart('-', $u_parts[$u_pos]);
-        $u_pos++;
-      } else if ($c == 'i') {
-        $diff->addPart('+', $v_parts[$v_pos]);
-        $v_pos++;
-      } else if ($c == 'x') {
-        $diff->addPart('-', $u_parts[$u_pos]);
-        $diff->addPart('+', $v_parts[$v_pos]);
-        $u_pos++;
-        $v_pos++;
-      } else {
-        throw new Exception(
-          pht(
-            'Unexpected character ("%s") in edit string.',
-            $c));
-      }
-    }
-
-    $diff->reorderParts();
-
-    // If we just built a character-level diff, we're all done and do not
-    // need to go any deeper.
-    if ($level == 3) {
-      return $diff;
-    }
-
-    $blocks = array();
-    $block = null;
-    foreach ($diff->getParts() as $part) {
-      $type = $part['type'];
-      $text = $part['text'];
-      switch ($type) {
-        case '=':
-          if ($block) {
-            $blocks[] = $block;
-            $block = null;
-          }
-          $blocks[] = array(
-            'type' => $type,
-            'text' => $text,
-          );
-          break;
-        case '-':
-          if (!$block) {
-            $block = array(
-              'type' => '!',
-              'old' => '',
-              'new' => '',
-            );
-          }
-          $block['old'] .= $text;
-          break;
-        case '+':
-          if (!$block) {
-            $block = array(
-              'type' => '!',
-              'old' => '',
-              'new' => '',
-            );
-          }
-          $block['new'] .= $text;
-          break;
-      }
-    }
-
-    if ($block) {
-      $blocks[] = $block;
-    }
-
-    $result = new PhutilProseDiff();
-    foreach ($blocks as $block) {
-      $type = $block['type'];
-      if ($type == '=') {
-        $result->addPart('=', $block['text']);
-      } else {
-        $old = $block['old'];
-        $new = $block['new'];
-        if (!strlen($old) && !strlen($new)) {
-          // Nothing to do.
-        } else if (!strlen($old)) {
-          $result->addPart('+', $new);
-        } else if (!strlen($new)) {
-          $result->addPart('-', $old);
-        } else {
-          if ($matrix->didReachMaximumLength()) {
-            // If this text was too big to diff, don't try to subdivide it.
-            $result->addPart('-', $old);
-            $result->addPart('+', $new);
-          } else {
-            $subdiff = $this->buildDiff(
-              $old,
-              $new,
-              $level + 1);
-
-            foreach ($subdiff->getParts() as $part) {
-              $result->addPart($part['type'], $part['text']);
-            }
-          }
-        }
-      }
-    }
-
-    $result->reorderParts();
-
-    return $result;
-  }
-
-  private function splitCorpus($corpus, $level) {
-    switch ($level) {
-      case 0:
-        // Level 0: Split into paragraphs.
-        $expr = '/([\n]+)/';
-        break;
-      case 1:
-        // Level 1: Split into sentences.
-        $expr = '/([\n,!;?\.]+)/';
-        break;
-      case 2:
-        // Level 2: Split into words.
-        $expr = '/(\s+)/';
-        break;
-      case 3:
-        // Level 3: Split into characters.
-        return phutil_utf8v_combined($corpus);
-    }
-
-    $pieces = preg_split($expr, $corpus, -1, PREG_SPLIT_DELIM_CAPTURE);
-    return $this->stitchPieces($pieces, $level);
-  }
-
-  private function stitchPieces(array $pieces, $level) {
-    $results = array();
-    $count = count($pieces);
-    for ($ii = 0; $ii < $count; $ii += 2) {
-      $result = $pieces[$ii];
-      if ($ii + 1 < $count) {
-        $result .= $pieces[$ii + 1];
-      }
-
-      if ($level < 2) {
-        // Split pieces into separate text and whitespace sections: make one
-        // piece out of all the whitespace at the beginning, one piece out of
-        // all the actual text in the middle, and one piece out of all the
-        // whitespace at the end.
-
-        $matches = null;
-        preg_match('/^(\s*)(.*?)(\s*)\z/', $result, $matches);
-
-        if (strlen($matches[1])) {
-          $results[] = $matches[1];
-        }
-        if (strlen($matches[2])) {
-          $results[] = $matches[2];
-        }
-        if (strlen($matches[3])) {
-          $results[] = $matches[3];
-        }
-      } else {
-        $results[] = $result;
-      }
-    }
-
-    // If the input ended with a delimiter, we can get an empty final piece.
-    // Just discard it.
-    if (last($results) == '') {
-      array_pop($results);
-    }
-
-    return $results;
-  }
-
-}
diff --git a/src/utils/__tests__/PhutilProseDiffTestCase.php b/src/utils/__tests__/PhutilProseDiffTestCase.php
deleted file mode 100644
--- a/src/utils/__tests__/PhutilProseDiffTestCase.php
+++ /dev/null
@@ -1,245 +0,0 @@
-<?php
-
-final class PhutilProseDiffTestCase extends PhutilTestCase {
-
-  public function testProseDiffsDistance() {
-    $this->assertProseParts(
-      '',
-      '',
-      array(),
-      pht('Empty'));
-
-    $this->assertProseParts(
-      "xxx\nyyy",
-      "xxx\nzzz\nyyy",
-      array(
-        "= xxx\n",
-        "+ zzz\n",
-        '= yyy',
-      ),
-      pht('Add Paragraph'));
-
-    $this->assertProseParts(
-      "xxx\nzzz\nyyy",
-      "xxx\nyyy",
-      array(
-        "= xxx\n",
-        "- zzz\n",
-        '= yyy',
-      ),
-      pht('Remove Paragraph'));
-
-
-    // Without smoothing, the alogorithm identifies that "shark" and "cat"
-    // both contain the letter "a" and tries to express this as a very
-    // fine-grained edit which replaces "sh" with "c" and then "rk" with "t".
-    // This is technically correct, but it is much easier for human viewers to
-    // parse if we smooth this into a single removal and a single addition.
-
-    $this->assertProseParts(
-      'They say the shark has nine lives.',
-      'They say the cat has nine lives.',
-      array(
-        '= They say the ',
-        '- shark',
-        '+ cat',
-        '=  has nine lives.',
-      ),
-      pht('"Shark/cat" word edit smoothenss.'));
-
-    $this->assertProseParts(
-      'Rising quickly, she says',
-      'Rising quickly, she remarks:',
-      array(
-        '= Rising quickly, she ',
-        '- says',
-        '+ remarks:',
-      ),
-      pht('"Says/remarks" word edit smoothenss.'));
-
-    $this->assertProseParts(
-      'See screenshots',
-      'Viewed video files',
-      array(
-        '- See screenshots',
-        '+ Viewed video files',
-      ),
-      pht('Complete paragraph rewrite.'));
-
-    $this->assertProseParts(
-      'xaaax',
-      'xbbbx',
-      array(
-        '- xaaax',
-        '+ xbbbx',
-      ),
-      pht('Whole word rewrite with common prefix and suffix.'));
-
-    $this->assertProseParts(
-      ' aaa ',
-      ' bbb ',
-      array(
-        '=  ',
-        '- aaa',
-        '+ bbb',
-        '=  ',
-      ),
-      pht('Whole word rewrite with whitespace prefix and suffix.'));
-
-    $this->assertSummaryProseParts(
-      "a\nb\nc\nd\ne\nf\ng\nh\n",
-      "a\nb\nc\nd\nX\nf\ng\nh\n",
-      array(
-        '.',
-        "= d\n",
-        '- e',
-        '+ X',
-        "= \nf",
-        '.',
-      ),
-      pht('Summary diff with middle change.'));
-
-    $this->assertSummaryProseParts(
-      "a\nb\nc\nd\ne\nf\ng\nh\n",
-      "X\nb\nc\nd\ne\nf\ng\nh\n",
-      array(
-        '- a',
-        '+ X',
-        "= \nb",
-        '.',
-      ),
-      pht('Summary diff with head change.'));
-
-    $this->assertSummaryProseParts(
-      "a\nb\nc\nd\ne\nf\ng\nh\n",
-      "a\nb\nc\nd\ne\nf\ng\nX\n",
-      array(
-        '.',
-        "= g\n",
-        '- h',
-        '+ X',
-        "= \n",
-      ),
-      pht('Summary diff with last change.'));
-
-    $this->assertProseParts(
-      'aaa aaa aaa aaa, bbb bbb bbb bbb.',
-      "aaa aaa aaa aaa, bbb bbb bbb bbb.\n\n- ccc ccc ccc",
-      array(
-        '= aaa aaa aaa aaa, bbb bbb bbb bbb.',
-        "+ \n\n- ccc ccc ccc",
-      ),
-      pht('Diff with new trailing content.'));
-
-    $this->assertProseParts(
-      'aaa aaa aaa aaa, bbb bbb bbb bbb.',
-      'aaa aaa aaa aaa bbb bbb bbb bbb.',
-      array(
-        '= aaa aaa aaa aaa',
-        '- ,',
-        '=  bbb bbb bbb bbb.',
-      ),
-      pht('Diff with a removed comma.'));
-
-    $this->assertProseParts(
-      'aaa aaa aaa aaa, bbb bbb bbb bbb.',
-      "aaa aaa aaa aaa bbb bbb bbb bbb.\n\n- ccc ccc ccc!",
-      array(
-        '= aaa aaa aaa aaa',
-        '- ,',
-        '=  bbb bbb bbb bbb.',
-        "+ \n\n- ccc ccc ccc!",
-      ),
-      pht('Diff with a removed comma and new trailing content.'));
-
-    $this->assertProseParts(
-      '[ ] Walnuts',
-      '[X] Walnuts',
-      array(
-        '= [',
-        '-  ',
-        '+ X',
-        '= ] Walnuts',
-      ),
-      pht('Diff adding a tickmark to a checkbox list.'));
-
-    $this->assertProseParts(
-      '[[ ./week49 ]]',
-      '[[ ./week50 ]]',
-      array(
-        '= [[ ./week',
-        '- 49',
-        '+ 50',
-        '=  ]]',
-      ),
-      pht('Diff changing a remarkup wiki link target.'));
-
-    // Create a large corpus with many sentences and paragraphs.
-    $large_paragraph = 'xyz. ';
-    $large_paragraph = str_repeat($large_paragraph, 50);
-    $large_paragraph = rtrim($large_paragraph);
-
-    $large_corpus = $large_paragraph."\n\n";
-    $large_corpus = str_repeat($large_corpus, 50);
-    $large_corpus = rtrim($large_corpus);
-
-    $this->assertProseParts(
-      $large_corpus,
-      "aaa\n\n".$large_corpus."\n\nzzz",
-      array(
-        "+ aaa\n\n",
-        '= '.$large_corpus,
-        "+ \n\nzzz",
-      ),
-      pht('Adding initial and final lines to a large corpus.'));
-
-  }
-
-  private function assertProseParts($old, $new, array $expect_parts, $label) {
-    $engine = new PhutilProseDifferenceEngine();
-    $diff = $engine->getDiff($old, $new);
-
-    $parts = $diff->getParts();
-
-    $this->assertParts($expect_parts, $parts, $label);
-  }
-
-  private function assertSummaryProseParts(
-    $old,
-    $new,
-    array $expect_parts,
-    $label) {
-
-    $engine = new PhutilProseDifferenceEngine();
-    $diff = $engine->getDiff($old, $new);
-
-    $parts = $diff->getSummaryParts();
-
-    $this->assertParts($expect_parts, $parts, $label);
-  }
-
-  private function assertParts(
-    array $expect,
-    array $actual_parts,
-    $label) {
-
-    $actual = array();
-    foreach ($actual_parts as $actual_part) {
-      $type = $actual_part['type'];
-      $text = $actual_part['text'];
-
-      switch ($type) {
-        case '.':
-          $actual[] = $type;
-          break;
-        default:
-          $actual[] = "{$type} {$text}";
-          break;
-      }
-    }
-
-    $this->assertEqual($expect, $actual, $label);
-  }
-
-
-}