diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3f2b5ce..390f8f7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Fixed
+
+-  Use `open()` instead of `codecs.open()`, which is deprecated in Python 3.14
+
 ## [0.28.0] - 2026-04-19
 
 ### Fixed
diff --git a/flattentool/__init__.py b/flattentool/__init__.py
index e293014..0cf1a57 100644
--- a/flattentool/__init__.py
+++ b/flattentool/__init__.py
@@ -1,4 +1,3 @@
-import codecs
 import datetime
 import json
 import sys
@@ -373,7 +372,7 @@ def unflatten(
         if output_name is None:
             sys.stdout.buffer.write(xml_output)
         else:
-            with codecs.open(output_name, "wb") as fp:
+            with open(output_name, "wb") as fp:
                 fp.write(xml_output)
     else:
         if output_name is None:
@@ -383,7 +382,7 @@ def unflatten(
                 )
             )
         else:
-            with codecs.open(output_name, "w", encoding="utf-8") as fp:
+            with open(output_name, "w", encoding="utf-8", newline="") as fp:
                 json.dump(
                     base,
                     fp,
@@ -392,7 +391,7 @@ def unflatten(
                     ensure_ascii=False,
                 )
     if cell_source_map:
-        with codecs.open(cell_source_map, "w", encoding="utf-8") as fp:
+        with open(cell_source_map, "w", encoding="utf-8", newline="") as fp:
             json.dump(
                 cell_source_map_data,
                 fp,
@@ -401,7 +400,7 @@ def unflatten(
                 ensure_ascii=False,
             )
     if heading_source_map:
-        with codecs.open(heading_source_map, "w", encoding="utf-8") as fp:
+        with open(heading_source_map, "w", encoding="utf-8", newline="") as fp:
             json.dump(
                 heading_source_map_data,
                 fp,
diff --git a/flattentool/json_input.py b/flattentool/json_input.py
index 414d003..e4ea855 100644
--- a/flattentool/json_input.py
+++ b/flattentool/json_input.py
@@ -5,7 +5,6 @@
 
 """
 
-import codecs
 import copy
 import os
 import tempfile
@@ -236,7 +235,7 @@ def __init__(
                 )
 
         if self.xml:
-            with codecs.open(json_filename, "rb") as xml_file:
+            with open(json_filename, "rb") as xml_file:
                 top_dict = xmltodict.parse(
                     xml_file,
                     force_list=(root_list_path,),
@@ -306,7 +305,7 @@ def __init__(
             else:
                 path = root_list_path.replace("/", ".") + ".item"
 
-            json_file = codecs.open(json_filename, "rb")
+            json_file = open(json_filename, "rb")
 
             self.root_json_list = ijson.items(json_file, path, map_type=OrderedDict)
 
diff --git a/flattentool/schema.py b/flattentool/schema.py
index 6c99212..b7a9710 100644
--- a/flattentool/schema.py
+++ b/flattentool/schema.py
@@ -2,7 +2,6 @@
 
 from __future__ import print_function, unicode_literals
 
-import codecs
 import os
 import sys
 from collections import OrderedDict, UserDict
@@ -163,7 +162,7 @@ def __init__(
                 )
             else:
                 if disable_local_refs:
-                    with codecs.open(schema_filename, encoding="utf-8") as schema_file:
+                    with open(schema_filename, encoding="utf-8") as schema_file:
                         self.root_schema_dict = jsonref.load(
                             schema_file,
                             object_pairs_hook=OrderedDict,
@@ -179,7 +178,7 @@ def __init__(
                             "file:",
                             urllib.pathname2url(os.path.abspath(schema_filename)),
                         )
-                    with codecs.open(schema_filename, encoding="utf-8") as schema_file:
+                    with open(schema_filename, encoding="utf-8") as schema_file:
                         self.root_schema_dict = jsonref.load(
                             schema_file,
                             object_pairs_hook=OrderedDict,