diff --git a/rosdistro_reviewer/yaml_lines.py b/rosdistro_reviewer/yaml_lines.py
new file mode 100644
index 0000000..076a156
--- /dev/null
+++ b/rosdistro_reviewer/yaml_lines.py
@@ -0,0 +1,98 @@
+# Copyright 2024 Open Source Robotics Foundation, Inc.
+# Licensed under the Apache License, Version 2.0
+
+import yaml
+
+
+class AnnotatedSafeLoader(yaml.SafeLoader):
+    """
+    YAML loader that adds '__lines__' attributes to some of the parsed data.
+
+    This extension of the PyYAML SafeLoader replaces some basic types with
+    derived types that include a '__lines__' attribute to determine where
+    the deserialized data can be found in the YAML file it was parsed from.
+    """
+
+    class AnnotatedDict(dict):
+        """Implementation of 'dict' with '__lines__' attribute."""
+
+        __slots__ = ('__lines__',)
+
+        def __init__(self, *args, **kwargs):  # noqa: D107
+            return super().__init__(*args, **kwargs)
+
+    class AnnotatedList(list):
+        """Implementation of 'list' with '__lines__' attribute."""
+
+        __slots__ = ('__lines__',)
+
+        def __init__(self, *args, **kwargs):  # noqa: D107
+            return super().__init__(*args, **kwargs)
+
+    class AnnotatedStr(str):
+        """Implementation of 'str' with '__lines__' attribute."""
+
+        __slots__ = ('__lines__',)
+
+        def __new__(cls, *args, **kwargs):  # noqa: D102
+            return str.__new__(cls, *args, **kwargs)
+
+    def compose_node(self, parent, index):  # noqa: D102
+        event = self.peek_event()
+        start_line = event.start_mark.line + 1
+        end_line = event.end_mark.line + 1
+        if end_line <= start_line:
+            end_line = start_line + 1
+        node = super().compose_node(parent, index)
+        node.__lines__ = range(start_line, end_line)
+        return node
+
+    def construct_annotated_map(self, node):  # noqa: D102
+        data = AnnotatedSafeLoader.AnnotatedDict()
+        data.__lines__ = node.__lines__
+        yield data
+        value = self.construct_mapping(node, deep=True)
+        for k, v in reversed(value.items()):
+            k_lines = getattr(k, '__lines__', None)
+            if k_lines is not None and k_lines.stop > data.__lines__.stop:
+                data.__lines__ = range(data.__lines__.start, k_lines.stop)
+
+            v_lines = getattr(v, '__lines__', None)
+            if v_lines is not None and v_lines.stop > data.__lines__.stop:
+                data.__lines__ = range(data.__lines__.start, v_lines.stop)
+        data.update(value)
+
+    def construct_annotated_seq(self, node):  # noqa: D102
+        data = AnnotatedSafeLoader.AnnotatedList()
+        data.__lines__ = node.__lines__
+        yield data
+        value = self.construct_sequence(node, deep=True)
+        for v in reversed(value):
+            v_lines = getattr(v, '__lines__', None)
+            if v_lines is not None and v_lines.stop > data.__lines__.stop:
+                data.__lines__ = range(data.__lines__.start, v_lines.stop)
+        data.extend(value)
+
+    def construct_annotated_str(self, node):  # noqa: D102
+        data = self.construct_yaml_str(node)
+        data = AnnotatedSafeLoader.AnnotatedStr(data)
+        data.__lines__ = node.__lines__
+        return data
+
+
+AnnotatedSafeLoader.add_constructor(
+    'tag:yaml.org,2002:map', AnnotatedSafeLoader.construct_annotated_map)
+AnnotatedSafeLoader.add_constructor(
+    'tag:yaml.org,2002:seq', AnnotatedSafeLoader.construct_annotated_seq)
+AnnotatedSafeLoader.add_constructor(
+    'tag:yaml.org,2002:str', AnnotatedSafeLoader.construct_annotated_str)
+
+yaml.add_representer(
+    AnnotatedSafeLoader.AnnotatedDict,
+    yaml.representer.SafeRepresenter.represent_dict)
+yaml.add_representer(
+    AnnotatedSafeLoader.AnnotatedList,
+    yaml.representer.SafeRepresenter.represent_list)
+yaml.add_representer(
+    AnnotatedSafeLoader.AnnotatedStr,
+    yaml.representer.SafeRepresenter.represent_str)
diff --git a/setup.cfg b/setup.cfg
index 1aa83a1..3dbbef5 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -22,6 +22,7 @@ python_requires = >=3.6
 install_requires =
     GitPython
     unidiff
+    PyYAML
 packages = find:
 zip_safe = true
 
@@ -31,6 +32,7 @@ test =
     mypy
     pytest
     scspell3k>=2.2
+    types-PyYAML
 
 [options.packages.find]
 exclude =
diff --git a/test/resources/simple.yaml b/test/resources/simple.yaml
new file mode 100644
index 0000000..56fb47b
--- /dev/null
+++ b/test/resources/simple.yaml
@@ -0,0 +1,13 @@
+---
+foo:
+  bar: baz
+  qux: [quux]
+  corge:
+    - grault
+    - garply
+  waldo: >-
+    Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
+    tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim
+    veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea
+    commodo consequat.
+  fred: null
diff --git a/test/spell_check.words b/test/spell_check.words
index ddc1c4f..9e66353 100644
--- a/test/spell_check.words
+++ b/test/spell_check.words
@@ -1,19 +1,26 @@
 addfinalizer
 apache
+corge
+deserialized
 diffs
+fred
 https
 iterdir
 linter
 mktemp
 mypy
+noqa
 patchset
 pathlib
 pycqa
 pytest
 rangeify
+representer
 returncode
 rosdistro
 scspell
 setuptools
 thomas
 unidiff
+waldo
+yaml
diff --git a/test/test_yaml_lines.py b/test/test_yaml_lines.py
new file mode 100644
index 0000000..1001f32
--- /dev/null
+++ b/test/test_yaml_lines.py
@@ -0,0 +1,51 @@
+# Copyright 2024 Open Source Robotics Foundation, Inc.
+# Licensed under the Apache License, Version 2.0
+
+from pathlib import Path
+
+from rosdistro_reviewer.yaml_lines import AnnotatedSafeLoader
+import yaml
+
+
+def _get_key_and_val(data, key):
+    for k, v in data.items():
+        if k == key:
+            return k, v
+    return None, None
+
+
+def test_line_numbers() -> None:
+    test_resources = Path(__file__).parent / 'resources'
+    test_yaml = test_resources / 'simple.yaml'
+    with test_yaml.open('r') as f:
+        test_data = yaml.load(f, Loader=AnnotatedSafeLoader)
+
+    foo, foo_val = _get_key_and_val(test_data, 'foo')
+    assert foo and foo.__lines__ == range(2, 3)
+    assert hasattr(foo_val, '__getitem__') and \
+        foo_val.__lines__ == range(3, 14)
+
+    bar, bar_val = _get_key_and_val(foo_val, 'bar')
+    assert bar and bar.__lines__ == range(3, 4)
+    assert bar_val == 'baz' and bar_val.__lines__ == range(3, 4)
+
+    qux, qux_val = _get_key_and_val(foo_val, 'qux')
+    assert qux and qux.__lines__ == range(4, 5)
+    assert hasattr(qux_val, '__iter__') and qux_val.__lines__ == range(4, 5)
+    for item in qux_val:
+        assert item.__lines__ == range(4, 5)
+
+    corge, corge_val = _get_key_and_val(foo_val, 'corge')
+    assert corge and corge.__lines__ == range(5, 6)
+    assert hasattr(corge_val, '__iter__') and \
+        corge_val.__lines__ == range(6, 8)
+    for idx, item in enumerate(corge_val):
+        assert item.__lines__ == range(6 + idx, 7 + idx)
+
+    waldo, waldo_val = _get_key_and_val(foo_val, 'waldo')
+    assert waldo and waldo.__lines__ == range(8, 9)
+    assert len(waldo_val) == 231 and waldo_val.__lines__ == range(8, 13)
+
+    fred, fred_val = _get_key_and_val(foo_val, 'fred')
+    assert fred and fred.__lines__ == range(13, 14)
+    assert fred_val is None