diff --git a/.pre-commit-hooks.yaml b/.pre-commit-hooks.yaml
index 3c82fc9..964de5d 100644
--- a/.pre-commit-hooks.yaml
+++ b/.pre-commit-hooks.yaml
@@ -2,10 +2,10 @@
   name: check LEGEND channel maps format
   entry: validate-legend-chmaps
   language: python
-  types: [json]
+  types: [yaml]
 
 - id: validate-legend-detdb
   name: check LEGEND detector database format
   entry: validate-legend-detdb
   language: python
-  types: [json]
+  types: [yaml]
diff --git a/docs/source/tutorial.rst b/docs/source/tutorial.rst
index f937009..08a5ed4 100644
--- a/docs/source/tutorial.rst
+++ b/docs/source/tutorial.rst
@@ -38,7 +38,7 @@ Let's consider the following database:
     │   └── file1.json
     ├── file2.json
     ├── file3.yaml
-    └── validity.jsonl
+    └── validity.yaml
 
 With:
 
@@ -80,20 +80,47 @@ Metadata validity
 -----------------
 
 Mappings of metadata to time periods, data taking systems etc. are specified
-through JSONL files (`specification
+through YAML files (`specification
 <https://legend-exp.github.io/legend-data-format-specs/dev/metadata>`_).
-If a ``.jsonl`` file is present in a directory, ``TextDB``
+If a ``validity.yaml`` file is present in a directory, ``TextDB``
 exposes the :meth:`~.textdb.textdb.on` interface to perform a query.
 
 Let's assume the ``legend-metadata`` directory from the example above contains
 the following file:
 
-.. code-block::
+.. code-block:: yaml
    :linenos:
-   :caption: ``validity.jsonl``
-
-   {"valid_from": "20220628T000000Z", "select": "all", "apply": ["file2.json"]}
-   {"valid_from": "20220629T000000Z", "select": "all", "apply": ["file3.yaml"]}
+   :caption: ``validity.yaml``
+
+   - valid_from: 20230101T000000Z
+      category: all
+      apply:
+         - file3.yaml
+
+   - valid_from: 20230102T000000Z
+      category: all
+      mode: append
+      apply:
+         - file2.yaml
+
+   - valid_from: 20230103T000000Z
+      category: all
+      mode: remove
+      apply:
+         - file2.yaml
+
+   - valid_from: 20230104T000000Z
+      category: all
+      mode: reset
+      apply:
+         - file2.yaml
+
+   - valid_from: 20230105T000000Z
+      category: all
+      mode: replace
+      apply:
+         - file2.yaml
+         - file3.yaml
 
 From code, it's possible to obtain the metadata valid for a certain time point:
 
diff --git a/src/legendmeta/catalog.py b/src/legendmeta/catalog.py
index 6299310..fa610fa 100644
--- a/src/legendmeta/catalog.py
+++ b/src/legendmeta/catalog.py
@@ -17,13 +17,14 @@
 import bisect
 import collections
 import copy
-import json
 import types
 from collections import namedtuple
 from datetime import datetime
 from pathlib import Path
 from string import Template
 
+import yaml
+
 from . import utils
 
 
@@ -33,6 +34,7 @@ def to_datetime(value):
 
 
 def unix_time(value):
+    """Convert a LEGEND timestamp or datetime object to Unix time value"""
     if isinstance(value, str):
         return datetime.timestamp(datetime.strptime(value, "%Y%m%dT%H%M%SZ"))
 
@@ -44,6 +46,8 @@ def unix_time(value):
 
 
 class PropsStream:
+    """Simple class to control loading of validity.yaml files"""
+
     @staticmethod
     def get(value):
         if isinstance(value, str):
@@ -57,13 +61,14 @@ def get(value):
 
     @staticmethod
     def read_from(file_name):
-        with Path(file_name).open() as file:
-            for json_str in file:
-                yield json.loads(json_str)
+        with Path(file_name).open() as r:
+            file = yaml.safe_load(r)
+        file = sorted(file, key=lambda item: unix_time(item["valid_from"]))
+        yield from file
 
 
 class Catalog(namedtuple("Catalog", ["entries"])):
-    """Implementation of the `JSONL metadata validity specification <https://legend-exp.github.io/legend-data-format-specs/dev/metadata/#Specifying-metadata-validity-in-time-(and-system)>`_."""
+    """Implementation of the `YAML metadata validity specification <https://legend-exp.github.io/legend-data-format-specs/dev/metadata/#Specifying-metadata-validity-in-time-(and-system)>`_."""
 
     __slots__ = ()
 
@@ -83,15 +88,40 @@ def get(value):
 
     @staticmethod
     def read_from(file_name):
+        """Read from a valdiity YAML file and build a Catalog object"""
         entries = {}
-
         for props in PropsStream.get(file_name):
             timestamp = props["valid_from"]
             system = "all" if props.get("category") is None else props["category"]
             file_key = props["apply"]
             if system not in entries:
                 entries[system] = []
-            entries[system].append(Catalog.Entry(unix_time(timestamp), file_key))
+            mode = "append" if props.get("mode") is None else props["mode"]
+            mode = "reset" if len(entries[system]) == 0 else mode
+            if mode == "reset":
+                new = file_key
+            elif mode == "append":
+                new = entries[system][-1].file.copy() + file_key
+            elif mode == "remove":
+                new = entries[system][-1].file.copy()
+                for file in file_key:
+                    new.remove(file)
+            elif mode == "replace":
+                new = entries[system][-1].file.copy()
+                if len(file_key) != 2:
+                    msg = f"Invalid number of elements in replace mode: {len(file_key)}"
+                    raise ValueError(msg)
+                new.remove(file_key[0])
+                new += [file_key[1]]
+
+            else:
+                msg = f"Unknown mode for {timestamp}"
+                raise ValueError(msg)
+
+            if timestamp in [entry.valid_from for entry in entries[system]]:
+                msg = f"Duplicate timestamp: {timestamp}, use reset mode instead with a single entry"
+                raise ValueError(msg)
+            entries[system].append(Catalog.Entry(unix_time(timestamp), new))
 
         for system in entries:
             entries[system] = sorted(
@@ -100,6 +130,7 @@ def read_from(file_name):
         return Catalog(entries)
 
     def valid_for(self, timestamp, system="all", allow_none=False):
+        """Get the valid entries for a given timestamp and system"""
         if system in self.entries:
             valid_from = [entry.valid_from for entry in self.entries[system]]
             pos = bisect.bisect_right(valid_from, unix_time(timestamp))
@@ -126,11 +157,14 @@ def valid_for(self, timestamp, system="all", allow_none=False):
 
     @staticmethod
     def get_files(catalog_file, timestamp, category="all"):
+        """Helper function to get the files for a given timestamp and category"""
         catalog = Catalog.read_from(catalog_file)
         return Catalog.valid_for(catalog, timestamp, category)
 
 
 class Props:
+    """Class to handle overwriting of dictionaries in cascade order"""
+
     @staticmethod
     def read_from(sources, subst_pathvar=False, trim_null=False):
         def read_impl(sources):
diff --git a/src/legendmeta/police.py b/src/legendmeta/police.py
index 57b10a0..9becbc6 100644
--- a/src/legendmeta/police.py
+++ b/src/legendmeta/police.py
@@ -16,12 +16,13 @@
 from __future__ import annotations
 
 import argparse
-import json
 import re
 import sys
 from importlib import resources
 from pathlib import Path
 
+import yaml
+
 from . import utils
 from .textdb import TextDB
 
@@ -96,10 +97,11 @@ def validate_legend_channel_map() -> bool:
         db = TextDB(d)
         valid = True
 
-        with Path(f"{d}/validity.jsonl").open() as f:
-            for line in f.readlines():
-                ts = json.loads(line)["valid_from"]
-                sy = json.loads(line)["select"]
+        with Path(f"{d}/validity.yaml").open() as f:
+            validity = yaml.safe_load(f)
+            for line in validity():
+                ts = line["valid_from"]
+                sy = line["apply"]
                 chmap = db.on(ts, system=sy)
 
                 for k, v in chmap.items():
diff --git a/src/legendmeta/textdb.py b/src/legendmeta/textdb.py
index e68a6d6..bc2b20b 100644
--- a/src/legendmeta/textdb.py
+++ b/src/legendmeta/textdb.py
@@ -381,11 +381,11 @@ def on(
     ) -> AttrsDict | list:
         """Query database in `time[, file pattern, system]`.
 
-        A (only one) valid ``validity.jsonl`` file must exist in the directory
+        A (only one) valid ``validity.yaml`` file must exist in the directory
         to specify a validity mapping. This functionality relies on the
         :class:`.catalog.Catalog` class.
 
-        The JSONL specification is documented at `this link
+        The YAML specification is documented at `this link
         <https://legend-exp.github.io/legend-data-format-specs/dev/metadata/#Specifying-metadata-validity-in-time-(and-system)>`_.
 
         The special ``$_`` string is expanded to the directory containing the
@@ -401,12 +401,15 @@ def on(
         system: 'all', 'phy', 'cal', 'lar', ...
             query only a data taking "system".
         """
-        jsonl = self.__path__ / "validity.jsonl"
-        if not jsonl.is_file():
-            msg = f"no validity.jsonl file found in {self.__path__!s}"
+        for ext in utils.__file_extensions__["yaml"]:
+            yml = self.__path__ / f"validity{ext}"
+            if yml.is_file():
+                break
+        if not yml.is_file():
+            msg = f"no validity.yaml / validity.yml file found in {self.__path__!s}"
             raise RuntimeError(msg)
 
-        file_list = Catalog.get_files(str(jsonl), timestamp, system)
+        file_list = Catalog.get_files(str(yml), timestamp, system)
         # select only files matching pattern if specified
         if pattern is not None:
             c = re.compile(pattern)
diff --git a/tests/test_jsondb.py b/tests/test_jsondb.py
index 7b5ef9e..484e007 100644
--- a/tests/test_jsondb.py
+++ b/tests/test_jsondb.py
@@ -19,7 +19,7 @@ def test_props():
     # test subst_vars
     Props.subst_vars(test_dict, var_values={"_": str(Path(__file__).parent / "testdb")})
     assert test_dict["filepath"] == str(
-        Path(__file__).parent / "testdb/dir1/file3.json"
+        Path(__file__).parent / "testdb/dir1/file3.yaml"
     )
 
     test_dict2 = Props.read_from(str(Path(__file__).parent / "testdb/file3.json"))
@@ -43,7 +43,7 @@ def test_props():
     )
     assert test_dict["data"] == 3
     assert test_dict["filepath"] == str(
-        Path(__file__).parent / "testdb/dir1/file3.json"
+        Path(__file__).parent / "testdb/dir1/file3.yaml"
     )
     with pytest.raises(KeyError):
         test_dict["null_key"]
@@ -55,12 +55,12 @@ def test_access():
     assert isinstance(jdb["file2.yaml"], AttrsDict)
     assert isinstance(jdb["file1"], AttrsDict)
     assert isinstance(jdb["dir1"], TextDB)
-    assert isinstance(jdb["dir1"]["file3.json"], AttrsDict)
+    assert isinstance(jdb["dir1"]["file3.yaml"], AttrsDict)
     assert isinstance(jdb["dir1"]["file3"], AttrsDict)
-    assert isinstance(jdb["dir1/file3.json"], AttrsDict)
+    assert isinstance(jdb["dir1/file3.yaml"], AttrsDict)
     assert isinstance(jdb["dir1"]["dir2"], TextDB)
-    assert isinstance(jdb["dir1"]["dir2"]["file4.json"], AttrsDict)
-    assert isinstance(jdb["dir1/dir2/file4.json"], AttrsDict)
+    assert isinstance(jdb["dir1"]["dir2"]["file4.yaml"], AttrsDict)
+    assert isinstance(jdb["dir1/dir2/file4.yaml"], AttrsDict)
     assert jdb["file1.json"]["data"] == 1
     assert isinstance(jdb["file1"]["group"], AttrsDict)
 
@@ -82,7 +82,7 @@ def test_access():
     assert jdb.arrays[1].array[0] == 1
     assert jdb.arrays[1].array[1].data == 2
 
-    assert jdb.file2.filepath == str(Path(__file__).parent / "testdb/dir1/file3.json")
+    assert jdb.file2.filepath == str(Path(__file__).parent / "testdb/dir1/file3.yaml")
 
     with pytest.raises(ValueError):
         TextDB("non-existent-db")
@@ -98,7 +98,7 @@ def test_access():
 def test_keys():
     jdb = TextDB(testdb, lazy=False)
     assert sorted(jdb.keys()) == ["arrays", "dir1", "dir2", "file1", "file2", "file3"]
-    assert sorted(jdb.dir1.keys()) == ["dir2", "file3", "file5"]
+    assert sorted(jdb.dir1.keys()) == ["dir2", "file3", "file5", "file6", "validity"]
 
     assert "arrays" in jdb
 
@@ -162,28 +162,33 @@ def test_scan():
 
 def test_time_validity():
     jdb = TextDB(testdb)
-    assert isinstance(jdb["dir1"].on("20220628T221955Z"), AttrsDict)
+    assert isinstance(jdb["dir1"].on("20230101T000001Z"), AttrsDict)
 
-    assert jdb["dir1"].on("20220628T221955Z")["data"] == 1
-    assert jdb.dir1.on("20220629T221955Z").data == 2
+    assert jdb["dir1"].on("20230101T000000Z")["data"] == 1
+    assert jdb.dir1.on("20230102T000000Z").data == 2
     # time point in between
-    assert jdb["dir1"].on("20220628T233500Z")["data"] == 1
+    assert jdb["dir1"].on("20230101T120000Z")["data"] == 1
     # time point after
-    assert jdb["dir1"].on("20220630T233500Z")["data"] == 2
+    assert jdb["dir1"].on("20230102T120000Z")["data"] == 2
     # time point before
     with pytest.raises(RuntimeError):
-        jdb["dir1"].on("20220627T233500Z")["data"]
-
-    # directory with no .jsonl
+        jdb["dir1"].on("20210101T000000Z")["data"]
+    # test remove functionality
+    assert jdb["dir1"].on("20230103T120000Z")["data"] == 1
+    # test reset functionality
+    assert jdb["dir1"].on("20230104T120000Z")["data"] == 3
+    # test replace functionality
+    assert jdb["dir1"].on("20230105T120000Z")["data"] == 1
+    # directory with no .yml
     with pytest.raises(RuntimeError):
-        jdb["dir1"]["dir2"].on("20220627T233500Z")
+        jdb["dir1"]["dir2"].on("20230101T000001Z")
 
     # invalid timestamp
     with pytest.raises(ValueError):
-        jdb.dir1.on("20220627T2335002Z")
+        jdb.dir1.on("20230627T2335002Z")
 
     # test usage of datetime object
-    tstamp = datetime(2022, 6, 28, 23, 35, 00, tzinfo=timezone.utc)
+    tstamp = datetime(2023, 6, 28, 23, 35, 00, tzinfo=timezone.utc)
     assert jdb.dir1.on(tstamp).data == 1
     assert jdb.dir1.on(tstamp, r"^file3.*", "all").data == 1
 
@@ -241,7 +246,15 @@ def test_merging():
     jdb = TextDB(testdb, lazy=False)
     j = jdb.dir1 | jdb.dir2
     assert isinstance(j, AttrsDict)
-    assert sorted(j.keys()) == ["dir2", "file3", "file5", "file7", "file8"]
+    assert sorted(j.keys()) == [
+        "dir2",
+        "file3",
+        "file5",
+        "file6",
+        "file7",
+        "file8",
+        "validity",
+    ]
     assert hasattr(j, "dir2")
     assert hasattr(j, "file8")
 
diff --git a/tests/testdb/dir1/file3.json b/tests/testdb/dir1/file3.json
deleted file mode 100644
index 858a13c..0000000
--- a/tests/testdb/dir1/file3.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "data": 1
-}
diff --git a/tests/testdb/dir1/file3.yaml b/tests/testdb/dir1/file3.yaml
new file mode 100644
index 0000000..937ac32
--- /dev/null
+++ b/tests/testdb/dir1/file3.yaml
@@ -0,0 +1 @@
+data: 1
diff --git a/tests/testdb/dir1/file5.json b/tests/testdb/dir1/file5.json
deleted file mode 100644
index 087e30f..0000000
--- a/tests/testdb/dir1/file5.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "data": 2
-}
diff --git a/tests/testdb/dir1/file5.yaml b/tests/testdb/dir1/file5.yaml
new file mode 100644
index 0000000..4182ac4
--- /dev/null
+++ b/tests/testdb/dir1/file5.yaml
@@ -0,0 +1 @@
+data: 2
diff --git a/tests/testdb/dir1/file6.yaml b/tests/testdb/dir1/file6.yaml
new file mode 100644
index 0000000..ebf3e8d
--- /dev/null
+++ b/tests/testdb/dir1/file6.yaml
@@ -0,0 +1 @@
+data: 3
diff --git a/tests/testdb/dir1/validity.jsonl b/tests/testdb/dir1/validity.jsonl
deleted file mode 100644
index 30c101f..0000000
--- a/tests/testdb/dir1/validity.jsonl
+++ /dev/null
@@ -1,2 +0,0 @@
-{"valid_from":"20220628T221955Z","select":"all","apply":["file3.json"]}
-{"valid_from":"20220629T221955Z","select":"all","apply":["file5.json"]}
diff --git a/tests/testdb/dir1/validity.yaml b/tests/testdb/dir1/validity.yaml
new file mode 100644
index 0000000..3604dc7
--- /dev/null
+++ b/tests/testdb/dir1/validity.yaml
@@ -0,0 +1,29 @@
+- valid_from: 20230101T000000Z
+  category: all
+  apply:
+    - file3.yaml
+
+- valid_from: 20230102T000000Z
+  category: all
+  mode: append
+  apply:
+    - file5.yaml
+
+- valid_from: 20230103T000000Z
+  category: all
+  mode: remove
+  apply:
+    - file5.yaml
+
+- valid_from: 20230104T000000Z
+  category: all
+  mode: reset
+  apply:
+    - file6.yaml
+
+- valid_from: 20230105T000000Z
+  category: all
+  mode: replace
+  apply:
+    - file6.yaml
+    - file3.yaml
diff --git a/tests/testdb/file2.yaml b/tests/testdb/file2.yaml
index 70e68b8..e7c6d8a 100644
--- a/tests/testdb/file2.yaml
+++ b/tests/testdb/file2.yaml
@@ -1,5 +1,5 @@
 data: 2
-filepath: $_/dir1/file3.json
+filepath: $_/dir1/file3.yaml
 key:
   label: 3
 label: 3