diff --git a/recipe_modules/roll_util/api.py b/recipe_modules/roll_util/api.py
new file mode 100644
index 0000000..61b6188
--- /dev/null
+++ b/recipe_modules/roll_util/api.py
@@ -0,0 +1,198 @@
+# Copyright 2020 The Pigweed Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License. You may obtain a copy of
+# the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations under
+# the License.
+"""Utility functions for rollers."""
+
+import pprint
+import re
+
+import attr
+from recipe_engine import recipe_api
+
+# If we're embedding the original commit message, prepend 'Original-' to lines
+# which begin with these tags.
+ESCAPE_TAGS = [
+    'Bug:',
+    'Fixed:',
+    'Reviewed-on:',
+]
+
+# If we're embedding the original commit message, remove lines which contain
+# these tags.
+FILTER_TAGS = [
+    'API-Review:',
+    'Acked-by:',
+    'CC:',
+    'CQ-Do-Not-Cancel-Tryjobs:',
+    'Change-Id:',
+    'Commit-Queue:',
+    'Reviewed-by:',
+    'Signed-off-by:',
+    'Testability-Review:',
+    'Tested-by:',
+]
+
+
+def _sanitize_message(message):
+    """Sanitize lines of a commit message.
+
+    Prepend 'Original-' to lines which begin with ESCAPE_TAGS. Filter
+    out lines which begin with FILTER_TAGS.
+    """
+    return '\n'.join(
+        "Original-" + line
+        if any((line.startswith(tag) for tag in ESCAPE_TAGS))
+        else line
+        for line in message.splitlines()
+        if not any((tag in line for tag in FILTER_TAGS))
+    )
+
+
+@attr.s
+class Commit(object):
+  hash = attr.ib()
+  message = attr.ib()
+
+
+def _is_hash(value):
+  return re.match(r'^[0-9a-fA-F]{40}', value)
+
+
+class RollUtilApi(recipe_api.RecipeApi):
+
+  def _single_commit_roll_message(self, project_name, commit,
+                                  old_revision, new_revision):
+    template = """
+[roll {project_name}] {sanitized_message}
+
+Rolled-Commits: {old_revision:.15}..{new_revision:.15}
+CQ-Do-Not-Cancel-Tryjobs: true
+    """.strip()
+
+    kwargs = {
+        'project_name': project_name,
+        'original_message': commit.message,
+        'sanitized_message': _sanitize_message(commit.message),
+        'old_revision': old_revision,
+        'new_revision': new_revision,
+    }
+
+    message = template.format(**kwargs)
+
+    with self.m.step.nest('message') as pres:
+      pres.logs['template'] = template
+      pres.logs['kwargs'] = pprint.pformat(kwargs)
+      pres.logs['message'] = message
+
+    return message
+
+  def _multiple_commits_roll_message(self, project_name, commits,
+                                     old_revision, new_revision):
+    template = """
+[{project_name}] Roll {number} commits
+
+{one_liners}
+
+Rolled-Commits: {old_revision:.15}..{new_revision:.15}
+CQ-Do-Not-Cancel-Tryjobs: true
+    """.strip()
+
+    one_liners = [
+        '{:.15} {}'.format(commit.hash, commit.message.splitlines()[0][:50])
+        for commit in commits
+    ]
+
+    number = len(commits)
+    if not _is_hash(old_revision):
+      number = 'multiple'
+      one_liners.append('...')
+
+    kwargs = {
+        'project_name': project_name,
+        'number': number,
+        'one_liners': '\n'.join(one_liners),
+        'old_revision': old_revision,
+        'new_revision': new_revision,
+    }
+
+    message = template.format(**kwargs)
+
+    with self.m.step.nest('message') as pres:
+      pres.logs['template'] = template
+      pres.logs['kwargs'] = pprint.pformat(kwargs)
+      pres.logs['message'] = message
+
+    return message
+
+  def _commits(self, proj_dir, old_revision, new_revision):
+    with self.m.context(cwd=proj_dir):
+      commits = []
+      if _is_hash(old_revision):
+        base = old_revision
+      else:
+        base = '{}~5'.format(new_revision)
+
+      for commit in self.m.git(
+          'log', '{}..{}'.format(base, new_revision),
+          '--pretty=format:%H %B', '-z',
+          stdout=self.m.raw_io.output()).stdout.strip('\0').split('\0'):
+        hash, message = commit.split(' ', 1)
+        commits.append(Commit(hash, message))
+      return commits
+
+  def message(self, project_name, proj_dir, old_revision, new_revision):
+    with self.m.step.nest('roll message'):
+      commits = self._commits(proj_dir, old_revision, new_revision)
+
+      if len(commits) > 1:
+        return self._multiple_commits_roll_message(
+            project_name, commits, old_revision, new_revision)
+
+      else:
+        return self._single_commit_roll_message(
+            project_name, commits[0], old_revision, new_revision)
+
+  def check_roll_direction(self, git_dir, old, new,
+                           name='check roll direction'):
+    """Return if old is an ancestor of new (i.e., the roll moves forward)."""
+    if old == new:
+      with self.m.step.nest(name) as pres:
+        pres.step_summary_text = 'up-to-date'
+      return False
+
+    with self.m.context(git_dir):
+      step = self.m.git(
+          'merge-base',
+          '--is-ancestor',
+          old,
+          new,
+          name=name,
+          ok_ret=(0, 1),
+      )
+
+      step.presentation.step_summary_text = 'backward'
+      if step.exc_result.retcode == 0:
+        step.presentation.step_summary_text = 'forward'
+
+      return step.exc_result.retcode == 0
+
+  def backwards_roll_step(self, remote, old_revision, new_revision):
+    with self.m.step.nest('cancelling roll') as pres:
+      fmt = ('not updating from {old} to {new} because {old} is newer '
+             'than {new}')
+      if old_revision == new_revision:
+        fmt = 'not updating from {old} to {new} because they are identical'
+      pres.step_summary_text = fmt.format(old=old_revision[0:7],
+                                          new=new_revision[0:7])
+      pres.links[old_revision] = '{}/+/{}'.format(remote, old_revision)
+      pres.links[new_revision] = '{}/+/{}'.format(remote, new_revision)