diff --git a/platformio/app.py b/platformio/app.py
index ae483f1f..e630dd3c 100644
--- a/platformio/app.py
+++ b/platformio/app.py
@@ -114,7 +114,7 @@ class State(object):
     def __exit__(self, type_, value, traceback):
         if self.modified:
             try:
-                with open(self.path, "w") as fp:
+                with open(self.path, mode="w", encoding="utf8") as fp:
                     fp.write(json.dumps(self._storage))
             except IOError:
                 raise exception.HomeDirPermissionsError(get_project_core_dir())
diff --git a/platformio/builder/main.py b/platformio/builder/main.py
index 5b09ad77..04d6e342 100644
--- a/platformio/builder/main.py
+++ b/platformio/builder/main.py
@@ -226,7 +226,11 @@ if set(["_idedata", "idedata"]) & set(COMMAND_LINE_TARGETS):
         projenv = env
     data = projenv.DumpIDEData(env)
     # dump to file for the further reading by project.helpers.load_project_ide_data
-    with open(projenv.subst(os.path.join("$BUILD_DIR", "idedata.json")), "w") as fp:
+    with open(
+        projenv.subst(os.path.join("$BUILD_DIR", "idedata.json")),
+        mode="w",
+        encoding="utf8",
+    ) as fp:
         json.dump(data, fp)
     click.echo("\n%s\n" % json.dumps(data))  # pylint: disable=undefined-variable
     env.Exit(0)
diff --git a/platformio/builder/tools/compilation_db.py b/platformio/builder/tools/compilation_db.py
index f91fa3ab..6dff1746 100644
--- a/platformio/builder/tools/compilation_db.py
+++ b/platformio/builder/tools/compilation_db.py
@@ -152,7 +152,7 @@ def WriteCompilationDb(target, source, env):
         item["file"] = os.path.abspath(item["file"])
         entries.append(item)
 
-    with open(str(target[0]), "w") as target_file:
+    with open(str(target[0]), mode="w", encoding="utf8") as target_file:
         json.dump(
             entries, target_file, sort_keys=True, indent=4, separators=(",", ": ")
         )
diff --git a/platformio/builder/tools/piolib.py b/platformio/builder/tools/piolib.py
index 3849a91b..aa4b2fe6 100644
--- a/platformio/builder/tools/piolib.py
+++ b/platformio/builder/tools/piolib.py
@@ -86,7 +86,9 @@ class LibBuilderFactory(object):
                     fname, piotool.SRC_BUILD_EXT + piotool.SRC_HEADER_EXT
                 ):
                     continue
-                with io.open(os.path.join(root, fname), errors="ignore") as fp:
+                with io.open(
+                    os.path.join(root, fname), encoding="utf8", errors="ignore"
+                ) as fp:
                     content = fp.read()
                 if not content:
                     continue
@@ -671,7 +673,7 @@ class MbedLibBuilder(LibBuilderBase):
 
     def _mbed_conf_append_macros(self, mbed_config_path, macros):
         lines = []
-        with open(mbed_config_path) as fp:
+        with open(mbed_config_path, encoding="utf8") as fp:
             for line in fp.readlines():
                 line = line.strip()
                 if line == "#endif":
@@ -690,7 +692,7 @@ class MbedLibBuilder(LibBuilderBase):
                 if len(tokens) < 2 or tokens[1] not in macros:
                     lines.append(line)
         lines.append("")
-        with open(mbed_config_path, "w") as fp:
+        with open(mbed_config_path, mode="w", encoding="utf8") as fp:
             fp.write("\n".join(lines))
 
 
diff --git a/platformio/builder/tools/piomaxlen.py b/platformio/builder/tools/piomaxlen.py
index 02622b9d..c7360418 100644
--- a/platformio/builder/tools/piomaxlen.py
+++ b/platformio/builder/tools/piomaxlen.py
@@ -65,7 +65,7 @@ def _file_long_data(env, data):
     )
     if os.path.isfile(tmp_file):
         return tmp_file
-    with open(tmp_file, "w") as fp:
+    with open(tmp_file, mode="w", encoding="utf8") as fp:
         fp.write(data)
     return tmp_file
 
diff --git a/platformio/builder/tools/piosize.py b/platformio/builder/tools/piosize.py
index e194511a..6ef8d945 100644
--- a/platformio/builder/tools/piosize.py
+++ b/platformio/builder/tools/piosize.py
@@ -37,7 +37,7 @@ def _run_tool(cmd, env, tool_args):
         makedirs(build_dir)
     tmp_file = join(build_dir, "size-data-longcmd.txt")
 
-    with open(tmp_file, "w") as fp:
+    with open(tmp_file, mode="w", encoding="utf8") as fp:
         fp.write("\n".join(tool_args))
 
     cmd.append("@" + tmp_file)
@@ -241,7 +241,9 @@ def DumpSizeData(_, target, source, env):  # pylint: disable=unused-argument
             file_data.update(v)
             data["memory"]["files"].append(file_data)
 
-    with open(join(env.subst("$BUILD_DIR"), "sizedata.json"), "w") as fp:
+    with open(
+        join(env.subst("$BUILD_DIR"), "sizedata.json"), mode="w", encoding="utf8"
+    ) as fp:
         fp.write(json.dumps(data))
 
 
diff --git a/platformio/cache.py b/platformio/cache.py
index 87377259..e8b7982d 100644
--- a/platformio/cache.py
+++ b/platformio/cache.py
@@ -78,9 +78,9 @@ class ContentCache(object):
         if not os.path.isdir(os.path.dirname(cache_path)):
             os.makedirs(os.path.dirname(cache_path))
         try:
-            with codecs.open(cache_path, "wb", encoding="utf8") as fp:
+            with codecs.open(cache_path, mode="wb", encoding="utf8") as fp:
                 fp.write(data)
-            with open(self._db_path, "a") as fp:
+            with open(self._db_path, mode="a", encoding="utf8") as fp:
                 fp.write("%s=%s\n" % (str(expire_time), os.path.basename(cache_path)))
         except UnicodeError:
             if os.path.isfile(cache_path):
@@ -102,7 +102,7 @@ class ContentCache(object):
         paths_for_delete = [self.get_cache_path(k) for k in keys]
         found = False
         newlines = []
-        with open(self._db_path) as fp:
+        with open(self._db_path, encoding="utf8") as fp:
             for line in fp.readlines():
                 line = line.strip()
                 if "=" not in line:
@@ -129,7 +129,7 @@ class ContentCache(object):
                         pass
 
         if found and self._lock_dbindex():
-            with open(self._db_path, "w") as fp:
+            with open(self._db_path, mode="w", encoding="utf8") as fp:
                 fp.write("\n".join(newlines) + "\n")
             self._unlock_dbindex()
 
diff --git a/platformio/commands/check/tools/pvsstudio.py b/platformio/commands/check/tools/pvsstudio.py
index e95e202c..36298d25 100644
--- a/platformio/commands/check/tools/pvsstudio.py
+++ b/platformio/commands/check/tools/pvsstudio.py
@@ -40,13 +40,13 @@ class PvsStudioCheckTool(CheckToolBase):  # pylint: disable=too-many-instance-at
         )
         super(PvsStudioCheckTool, self).__init__(*args, **kwargs)
 
-        with open(self._tmp_cfg_file, "w") as fp:
+        with open(self._tmp_cfg_file, mode="w", encoding="utf8") as fp:
             fp.write(
                 "exclude-path = "
                 + self.config.get_optional_dir("packages").replace("\\", "/")
             )
 
-        with open(self._tmp_cmd_file, "w") as fp:
+        with open(self._tmp_cmd_file, mode="w", encoding="utf8") as fp:
             fp.write(
                 " ".join(
                     ['-I"%s"' % inc.replace("\\", "/") for inc in self.cpp_includes]
diff --git a/platformio/commands/home/rpc/handlers/project.py b/platformio/commands/home/rpc/handlers/project.py
index 8bac4d1c..2263beb1 100644
--- a/platformio/commands/home/rpc/handlers/project.py
+++ b/platformio/commands/home/rpc/handlers/project.py
@@ -261,7 +261,7 @@ class ProjectRPC:
                 return project_dir
             if not os.path.isdir(src_dir):
                 os.makedirs(src_dir)
-            with open(main_path, "w") as fp:
+            with open(main_path, mode="w", encoding="utf8") as fp:
                 fp.write(main_content.strip())
         return project_dir
 
diff --git a/platformio/commands/project.py b/platformio/commands/project.py
index e7809e25..d45d6dcd 100644
--- a/platformio/commands/project.py
+++ b/platformio/commands/project.py
@@ -240,7 +240,7 @@ def init_base_project(project_dir):
 
 
 def init_include_readme(include_dir):
-    with open(os.path.join(include_dir, "README"), "w") as fp:
+    with open(os.path.join(include_dir, "README"), mode="w", encoding="utf8") as fp:
         fp.write(
             """
 This directory is intended for project header files.
@@ -286,7 +286,7 @@ https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html
 
 
 def init_lib_readme(lib_dir):
-    with open(os.path.join(lib_dir, "README"), "w") as fp:
+    with open(os.path.join(lib_dir, "README"), mode="w", encoding="utf8") as fp:
         fp.write(
             """
 This directory is intended for project specific (private) libraries.
@@ -339,7 +339,7 @@ More information about PlatformIO Library Dependency Finder
 
 
 def init_test_readme(test_dir):
-    with open(os.path.join(test_dir, "README"), "w") as fp:
+    with open(os.path.join(test_dir, "README"), mode="w", encoding="utf8") as fp:
         fp.write(
             """
 This directory is intended for PlatformIO Unit Testing and project tests.
@@ -360,7 +360,7 @@ def init_cvs_ignore(project_dir):
     conf_path = os.path.join(project_dir, ".gitignore")
     if os.path.isfile(conf_path):
         return
-    with open(conf_path, "w") as fp:
+    with open(conf_path, mode="w", encoding="utf8") as fp:
         fp.write(".pio\n")
 
 
diff --git a/platformio/commands/remote/client/device_monitor.py b/platformio/commands/remote/client/device_monitor.py
index 990bb433..4c68f85f 100644
--- a/platformio/commands/remote/client/device_monitor.py
+++ b/platformio/commands/remote/client/device_monitor.py
@@ -173,7 +173,11 @@ class DeviceMonitorClient(  # pylint: disable=too-many-instance-attributes
         address = port.getHost()
         self.log.debug("Serial Bridge is started on {address!r}", address=address)
         if "sock" in self.cmd_options:
-            with open(os.path.join(self.cmd_options["sock"], "sock"), "w") as fp:
+            with open(
+                os.path.join(self.cmd_options["sock"], "sock"),
+                mode="w",
+                encoding="utf8",
+            ) as fp:
                 fp.write("socket://localhost:%d" % address.port)
 
     def client_terminal_stopped(self):
diff --git a/platformio/commands/remote/command.py b/platformio/commands/remote/command.py
index edf6b077..f9486d51 100644
--- a/platformio/commands/remote/command.py
+++ b/platformio/commands/remote/command.py
@@ -350,7 +350,7 @@ def device_monitor(ctx, agents, **kwargs):
             sleep(0.1)
         if not t.is_alive():
             return
-        with open(sock_file) as fp:
+        with open(sock_file, encoding="utf8") as fp:
             kwargs["port"] = fp.read()
         ctx.invoke(cmd_device_monitor, **kwargs)
         t.join(2)
diff --git a/platformio/commands/run/helpers.py b/platformio/commands/run/helpers.py
index ab362c24..c976d935 100644
--- a/platformio/commands/run/helpers.py
+++ b/platformio/commands/run/helpers.py
@@ -54,11 +54,11 @@ def clean_build_dir(build_dir, config):
     if isdir(build_dir):
         # check project structure
         if isfile(checksum_file):
-            with open(checksum_file) as fp:
+            with open(checksum_file, encoding="utf8") as fp:
                 if fp.read() == checksum:
                     return
         fs.rmtree(build_dir)
 
     makedirs(build_dir)
-    with open(checksum_file, "w") as fp:
+    with open(checksum_file, mode="w", encoding="utf8") as fp:
         fp.write(checksum)
diff --git a/platformio/commands/system/completion.py b/platformio/commands/system/completion.py
index 1a969203..012df5fc 100644
--- a/platformio/commands/system/completion.py
+++ b/platformio/commands/system/completion.py
@@ -42,7 +42,7 @@ def is_completion_code_installed(shell, path):
 
     import click_completion  # pylint: disable=import-error,import-outside-toplevel
 
-    with open(path) as fp:
+    with open(path, encoding="utf8") as fp:
         return click_completion.get_code(shell=shell) in fp.read()
 
 
@@ -64,7 +64,7 @@ def uninstall_completion_code(shell, path):
 
     import click_completion  # pylint: disable=import-error,import-outside-toplevel
 
-    with open(path, "r+") as fp:
+    with open(path, "r+", encoding="utf8") as fp:
         contents = fp.read()
         fp.seek(0)
         fp.truncate()
diff --git a/platformio/commands/test/processor.py b/platformio/commands/test/processor.py
index ea975e62..3e9a519d 100644
--- a/platformio/commands/test/processor.py
+++ b/platformio/commands/test/processor.py
@@ -224,7 +224,7 @@ class TestProcessorBase(object):
             test_dir,
             "%s.%s" % (tmp_file_prefix, transport_options.get("language", "c")),
         )
-        with open(tmp_file, "w") as fp:
+        with open(tmp_file, mode="w", encoding="utf8") as fp:
             fp.write(data)
 
         atexit.register(delete_tmptest_files, test_dir)
diff --git a/platformio/commands/upgrade.py b/platformio/commands/upgrade.py
index d8f6e78c..66eda804 100644
--- a/platformio/commands/upgrade.py
+++ b/platformio/commands/upgrade.py
@@ -103,7 +103,7 @@ def get_pip_package(to_develop):
         os.makedirs(cache_dir)
     pkg_name = os.path.join(cache_dir, "piocoredevelop.zip")
     try:
-        with open(pkg_name, "w") as fp:
+        with open(pkg_name, "w", encoding="utf8") as fp:
             r = exec_command(
                 ["curl", "-fsSL", dl_url], stdout=fp, universal_newlines=True
             )
diff --git a/platformio/debug/helpers.py b/platformio/debug/helpers.py
index 6b4d4278..5bac5d61 100644
--- a/platformio/debug/helpers.py
+++ b/platformio/debug/helpers.py
@@ -154,11 +154,11 @@ def is_prog_obsolete(prog_path):
     new_digest = shasum.hexdigest()
     old_digest = None
     if isfile(prog_hash_path):
-        with open(prog_hash_path) as fp:
+        with open(prog_hash_path, encoding="utf8") as fp:
             old_digest = fp.read()
     if new_digest == old_digest:
         return False
-    with open(prog_hash_path, "w") as fp:
+    with open(prog_hash_path, mode="w", encoding="utf8") as fp:
         fp.write(new_digest)
     return True
 
diff --git a/platformio/debug/process/gdb.py b/platformio/debug/process/gdb.py
index 836c637f..079b8b53 100644
--- a/platformio/debug/process/gdb.py
+++ b/platformio/debug/process/gdb.py
@@ -105,7 +105,7 @@ class GDBClientProcess(DebugClientProcess):
         footer = ["echo %s\\n" % self.INIT_COMPLETED_BANNER]
         commands = banner + commands + footer
 
-        with open(dst, "w") as fp:
+        with open(dst, mode="w", encoding="utf8") as fp:
             fp.write("\n".join(self.debug_config.reveal_patterns(commands)))
 
     def stdin_data_received(self, data):
diff --git a/platformio/fs.py b/platformio/fs.py
index 655c2ee8..258fe530 100644
--- a/platformio/fs.py
+++ b/platformio/fs.py
@@ -52,7 +52,7 @@ def get_source_dir():
 
 def load_json(file_path):
     try:
-        with open(file_path, "r") as f:
+        with open(file_path, mode="r", encoding="utf8") as f:
             return json.load(f)
     except ValueError:
         raise exception.InvalidJSONFile(file_path)
@@ -102,7 +102,7 @@ def ensure_udev_rules():
 
     def _rules_to_set(rules_path):
         result = set()
-        with open(rules_path) as fp:
+        with open(rules_path, encoding="utf8") as fp:
             for line in fp.readlines():
                 line = line.strip()
                 if not line or line.startswith("#"):
diff --git a/platformio/package/lockfile.py b/platformio/package/lockfile.py
index 6cfc46ef..8d6c837c 100644
--- a/platformio/package/lockfile.py
+++ b/platformio/package/lockfile.py
@@ -62,7 +62,9 @@ class LockFile(object):
             else:
                 raise LockFileExists
 
-        self._fp = open(self._lock_path, "w")  # pylint: disable=consider-using-with
+        self._fp = open(
+            self._lock_path, mode="w", encoding="utf8"
+        )  # pylint: disable=consider-using-with
         try:
             if LOCKFILE_CURRENT_INTERFACE == LOCKFILE_INTERFACE_FCNTL:
                 fcntl.flock(self._fp.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
diff --git a/platformio/package/manager/core.py b/platformio/package/manager/core.py
index 63251af3..270ce8e6 100644
--- a/platformio/package/manager/core.py
+++ b/platformio/package/manager/core.py
@@ -156,7 +156,9 @@ def build_contrib_pysite_package(target_dir, with_metadata=True):
         subprocess.check_call(args + [dep])
 
     # build manifests
-    with open(os.path.join(target_dir, "package.json"), "w") as fp:
+    with open(
+        os.path.join(target_dir, "package.json"), mode="w", encoding="utf8"
+    ) as fp:
         json.dump(
             dict(
                 name="contrib-pysite",
diff --git a/platformio/package/manager/library.py b/platformio/package/manager/library.py
index 3f77846b..03960306 100644
--- a/platformio/package/manager/library.py
+++ b/platformio/package/manager/library.py
@@ -44,7 +44,9 @@ class LibraryPackageManager(BasePackageManager):  # pylint: disable=too-many-anc
         root_dir = self.find_library_root(path)
 
         # automatically generate library manifest
-        with open(os.path.join(root_dir, "library.json"), "w") as fp:
+        with open(
+            os.path.join(root_dir, "library.json"), mode="w", encoding="utf8"
+        ) as fp:
             json.dump(
                 dict(
                     name=spec.name,
diff --git a/platformio/package/meta.py b/platformio/package/meta.py
index 74af1916..309c5fd8 100644
--- a/platformio/package/meta.py
+++ b/platformio/package/meta.py
@@ -382,12 +382,12 @@ class PackageMetaData(object):
         )
 
     def dump(self, path):
-        with open(path, "w") as fp:
+        with open(path, mode="w", encoding="utf8") as fp:
             return json.dump(self.as_dict(), fp)
 
     @staticmethod
     def load(path):
-        with open(path) as fp:
+        with open(path, encoding="utf8") as fp:
             data = json.load(fp)
             if data["spec"]:
                 data["spec"] = PackageSpec(**data["spec"])
diff --git a/platformio/package/pack.py b/platformio/package/pack.py
index 6644311c..8688d171 100644
--- a/platformio/package/pack.py
+++ b/platformio/package/pack.py
@@ -181,7 +181,9 @@ class PackagePacker(object):
             and os.path.isdir(os.path.join(src, include[0]))
         ):
             src = os.path.join(src, include[0])
-            with open(os.path.join(src, "library.json"), "w") as fp:
+            with open(
+                os.path.join(src, "library.json"), mode="w", encoding="utf8"
+            ) as fp:
                 manifest_updated = manifest.copy()
                 del manifest_updated["export"]["include"]
                 json.dump(manifest_updated, fp, indent=2, ensure_ascii=False)
diff --git a/platformio/proc.py b/platformio/proc.py
index 93be151b..0484cc42 100644
--- a/platformio/proc.py
+++ b/platformio/proc.py
@@ -158,7 +158,7 @@ def is_container():
         return True
     if not os.path.isfile("/proc/1/cgroup"):
         return False
-    with open("/proc/1/cgroup") as fp:
+    with open("/proc/1/cgroup", encoding="utf8") as fp:
         return ":/docker/" in fp.read()
 
 
diff --git a/platformio/project/config.py b/platformio/project/config.py
index 0d100507..13ff8e2b 100644
--- a/platformio/project/config.py
+++ b/platformio/project/config.py
@@ -456,7 +456,7 @@ class ProjectConfig(ProjectConfigBase, ProjectConfigDirsMixin):
         path = path or self.path
         if path in self._instances:
             del self._instances[path]
-        with open(path or self.path, "w+") as fp:
+        with open(path or self.path, mode="w+", encoding="utf8") as fp:
             fp.write(CONFIG_HEADER.strip() + "\n\n")
             self._parser.write(fp)
             fp.seek(0)
diff --git a/platformio/project/helpers.py b/platformio/project/helpers.py
index c41744a1..655e9685 100644
--- a/platformio/project/helpers.py
+++ b/platformio/project/helpers.py
@@ -177,6 +177,6 @@ def _load_cached_project_ide_data(project_dir, env_names):
     for name in env_names:
         if not os.path.isfile(os.path.join(build_dir, name, "idedata.json")):
             continue
-        with open(os.path.join(build_dir, name, "idedata.json")) as fp:
+        with open(os.path.join(build_dir, name, "idedata.json"), encoding="utf8") as fp:
             result[name] = json.load(fp)
     return result
diff --git a/tests/package/test_manager.py b/tests/package/test_manager.py
index 920aee04..19d4a98e 100644
--- a/tests/package/test_manager.py
+++ b/tests/package/test_manager.py
@@ -46,7 +46,7 @@ def test_download(isolated_pio_core):
     lm.cleanup_expired_downloads()
     assert not os.path.isfile(archive_path)
     # check that key is deleted from DB
-    with open(lm.get_download_usagedb_path()) as fp:
+    with open(lm.get_download_usagedb_path(), encoding="utf8") as fp:
         assert os.path.basename(archive_path) not in fp.read()