diff --git a/src/py/flwr/common/constant.py b/src/py/flwr/common/constant.py
index f1495958945..3f828098482 100644
--- a/src/py/flwr/common/constant.py
+++ b/src/py/flwr/common/constant.py
@@ -106,3 +106,26 @@ class ErrorCode:
     def __new__(cls) -> ErrorCode:
         """Prevent instantiation."""
         raise TypeError(f"{cls.__name__} cannot be instantiated.")
+
+
+class Record:
+    """Keys for records in a RecordSet."""
+
+    PARAMS = "p"
+    METRICS = "m"
+    CONFIGS = "c"
+
+    def __new__(cls) -> Record:
+        """Prevent instantiation."""
+        raise TypeError(f"{cls.__name__} cannot be instantiated.")
+
+
+class Metric:
+    """Keys for metrics in a MetricsRecord."""
+
+    NUM_EXAMPLES = "num_examples"
+    LOSS = "loss"
+
+    def __new__(cls) -> Metric:
+        """Prevent instantiation."""
+        raise TypeError(f"{cls.__name__} cannot be instantiated.")
diff --git a/src/py/flwr/common/record/recordset.py b/src/py/flwr/common/record/recordset.py
index 74eed46ad86..9c17152c81a 100644
--- a/src/py/flwr/common/record/recordset.py
+++ b/src/py/flwr/common/record/recordset.py
@@ -15,14 +15,63 @@
 """RecordSet."""
 
 
+from __future__ import annotations
+
 from dataclasses import dataclass
-from typing import Dict, Optional, cast
+from typing import Literal, TypeVar, cast, overload
 
+from ..constant import Record
 from .configsrecord import ConfigsRecord
 from .metricsrecord import MetricsRecord
 from .parametersrecord import ParametersRecord
 from .typeddict import TypedDict
 
+T = TypeVar("T", ParametersRecord, MetricsRecord, ConfigsRecord)
+
+
+class _Checker:
+    def __init__(
+        self,
+        data: RecordSetData,
+        r_type: type[ParametersRecord] | type[MetricsRecord] | type[ConfigsRecord],
+    ) -> None:
+        self.data = data
+        self._type = r_type
+
+    def check_key(self, key: str) -> None:
+        """Check the validity of the key."""
+        data = self.data
+        if not isinstance(key, str):
+            raise TypeError(
+                f"Expected `{str.__name__}`, but "
+                f"received `{type(key).__name__}` for the key."
+            )
+
+        orig_value: ParametersRecord | MetricsRecord | ConfigsRecord | None = None
+        if key in data.parameters_records:
+            orig_value = data.parameters_records[key]
+        elif key in data.metrics_records:
+            orig_value = data.metrics_records[key]
+        elif key in data.configs_records:
+            orig_value = data.configs_records[key]
+
+        if orig_value is not None and not isinstance(orig_value, self._type):
+            raise TypeError(
+                f"Key '{key}' is already associated with "
+                f"a '{type(orig_value).__name__}', but a value "
+                f"of type '{self._type.__name__}' was provided."
+            )
+
+    def check_value(
+        self, value: ParametersRecord | MetricsRecord | ConfigsRecord
+    ) -> None:
+        """Check the validity of the value."""
+        if not isinstance(value, self._type):
+            raise TypeError(
+                f"Expected `{self._type.__name__}`, but received "
+                f"`{type(value).__name__}` for the value."
+            )
+
 
 @dataclass
 class RecordSetData:
@@ -34,18 +83,21 @@ class RecordSetData:
 
     def __init__(
         self,
-        parameters_records: Optional[Dict[str, ParametersRecord]] = None,
-        metrics_records: Optional[Dict[str, MetricsRecord]] = None,
-        configs_records: Optional[Dict[str, ConfigsRecord]] = None,
+        parameters_records: dict[str, ParametersRecord] | None = None,
+        metrics_records: dict[str, MetricsRecord] | None = None,
+        configs_records: dict[str, ConfigsRecord] | None = None,
     ) -> None:
+        params_checker = _Checker(self, ParametersRecord)
+        metrics_checker = _Checker(self, MetricsRecord)
+        configs_checker = _Checker(self, ConfigsRecord)
         self.parameters_records = TypedDict[str, ParametersRecord](
-            self._check_fn_str, self._check_fn_params
+            params_checker.check_key, params_checker.check_value
         )
         self.metrics_records = TypedDict[str, MetricsRecord](
-            self._check_fn_str, self._check_fn_metrics
+            metrics_checker.check_key, metrics_checker.check_value
         )
         self.configs_records = TypedDict[str, ConfigsRecord](
-            self._check_fn_str, self._check_fn_configs
+            configs_checker.check_key, configs_checker.check_value
         )
         if parameters_records is not None:
             self.parameters_records.update(parameters_records)
@@ -54,43 +106,15 @@ def __init__(
         if configs_records is not None:
             self.configs_records.update(configs_records)
 
-    def _check_fn_str(self, key: str) -> None:
-        if not isinstance(key, str):
-            raise TypeError(
-                f"Expected `{str.__name__}`, but "
-                f"received `{type(key).__name__}` for the key."
-            )
-
-    def _check_fn_params(self, record: ParametersRecord) -> None:
-        if not isinstance(record, ParametersRecord):
-            raise TypeError(
-                f"Expected `{ParametersRecord.__name__}`, but "
-                f"received `{type(record).__name__}` for the value."
-            )
-
-    def _check_fn_metrics(self, record: MetricsRecord) -> None:
-        if not isinstance(record, MetricsRecord):
-            raise TypeError(
-                f"Expected `{MetricsRecord.__name__}`, but "
-                f"received `{type(record).__name__}` for the value."
-            )
-
-    def _check_fn_configs(self, record: ConfigsRecord) -> None:
-        if not isinstance(record, ConfigsRecord):
-            raise TypeError(
-                f"Expected `{ConfigsRecord.__name__}`, but "
-                f"received `{type(record).__name__}` for the value."
-            )
-
 
 class RecordSet:
     """RecordSet stores groups of parameters, metrics and configs."""
 
     def __init__(
         self,
-        parameters_records: Optional[Dict[str, ParametersRecord]] = None,
-        metrics_records: Optional[Dict[str, MetricsRecord]] = None,
-        configs_records: Optional[Dict[str, ConfigsRecord]] = None,
+        parameters_records: dict[str, ParametersRecord] | None = None,
+        metrics_records: dict[str, MetricsRecord] | None = None,
+        configs_records: dict[str, ConfigsRecord] | None = None,
     ) -> None:
         data = RecordSetData(
             parameters_records=parameters_records,
@@ -117,6 +141,69 @@ def configs_records(self) -> TypedDict[str, ConfigsRecord]:
         data = cast(RecordSetData, self.__dict__["_data"])
         return data.configs_records
 
+    @overload
+    def __getitem__(self, key: Literal["p"]) -> ParametersRecord: ...  # noqa: E704
+
+    @overload
+    def __getitem__(self, key: Literal["m"]) -> MetricsRecord: ...  # noqa: E704
+
+    @overload
+    def __getitem__(self, key: Literal["c"]) -> ConfigsRecord: ...  # noqa: E704
+
+    def __getitem__(self, key: str) -> ParametersRecord | MetricsRecord | ConfigsRecord:
+        """Return the record for the specified key."""
+        # Initialize default *Record
+        data = cast(RecordSetData, self.__dict__["_data"])
+        if key == Record.PARAMS and key not in data.parameters_records:
+            data.parameters_records[key] = ParametersRecord()
+        elif key == Record.METRICS and key not in data.metrics_records:
+            data.metrics_records[key] = MetricsRecord()
+        elif key == Record.CONFIGS and key not in data.configs_records:
+            data.configs_records[key] = ConfigsRecord()
+
+        # Return the record
+        if key in data.parameters_records:
+            return data.parameters_records[key]
+        if key in data.metrics_records:
+            return data.metrics_records[key]
+        if key in data.configs_records:
+            return data.configs_records[key]
+        raise KeyError(key)
+
+    def __setitem__(
+        self, key: str, value: ParametersRecord | MetricsRecord | ConfigsRecord
+    ) -> None:
+        """Set the record for the specified key."""
+        data = cast(RecordSetData, self.__dict__["_data"])
+        builtin_key_name: str | None = None
+        record_type: (
+            type[ParametersRecord] | type[MetricsRecord] | type[ConfigsRecord] | None
+        ) = None
+        if key == Record.PARAMS:
+            builtin_key_name, record_type = "Record.PARAMS", ParametersRecord
+        elif key == Record.METRICS:
+            builtin_key_name, record_type = "Record.METRICS", MetricsRecord
+        elif key == Record.CONFIGS:
+            builtin_key_name, record_type = "Record.CONFIGS", ConfigsRecord
+        if record_type is not None and not isinstance(value, record_type):
+            raise TypeError(
+                f"Expected value of type `{record_type.__name__}` for built-in key "
+                f"`{builtin_key_name}`, but received type `{type(value).__name__}`."
+            )
+
+        if isinstance(value, ParametersRecord):
+            data.parameters_records[key] = value
+        elif isinstance(value, MetricsRecord):
+            data.metrics_records[key] = value
+        elif isinstance(value, ConfigsRecord):
+            data.configs_records[key] = value
+        else:
+            raise TypeError(
+                f"Expected {{`{ParametersRecord.__name__}`, "
+                f"`{MetricsRecord.__name__}`, `{ConfigsRecord.__name__}`}}, "
+                f"but received `{type(value).__name__}` for the value."
+            )
+
     def __repr__(self) -> str:
         """Return a string representation of this instance."""
         flds = ("parameters_records", "metrics_records", "configs_records")
diff --git a/src/py/flwr/common/record/recordset_test.py b/src/py/flwr/common/record/recordset_test.py
index 01260793cb4..91507ceaa2f 100644
--- a/src/py/flwr/common/record/recordset_test.py
+++ b/src/py/flwr/common/record/recordset_test.py
@@ -17,11 +17,12 @@
 import pickle
 from collections import namedtuple
 from copy import deepcopy
-from typing import Callable, Dict, List, OrderedDict, Type, Union
+from typing import Any, Callable, Dict, List, OrderedDict, Type, Union
 
 import numpy as np
 import pytest
 
+from flwr.common.constant import Record
 from flwr.common.parameter import ndarrays_to_parameters, parameters_to_ndarrays
 from flwr.common.recordset_compat import (
     parameters_to_parametersrecord,
@@ -430,3 +431,29 @@ def test_recordset_repr() -> None:
 
     # Assert
     assert str(rs) == str(expected)
+
+
+@pytest.mark.parametrize(
+    "rs, key, value, exc_type",
+    [
+        # Invalid key type
+        (RecordSet(), 12, ConfigsRecord(), TypeError),
+        # Invalid value type
+        (RecordSet(), "resnet", 0.9, TypeError),
+        # Invalid record type for built-in keys
+        (RecordSet(), Record.PARAMS, MetricsRecord(), TypeError),
+        (RecordSet(), Record.PARAMS, ConfigsRecord(), TypeError),
+        (RecordSet(), Record.METRICS, ParametersRecord(), TypeError),
+        (RecordSet(), Record.METRICS, ConfigsRecord(), TypeError),
+        (RecordSet(), Record.CONFIGS, ParametersRecord(), TypeError),
+        (RecordSet(), Record.CONFIGS, MetricsRecord(), TypeError),
+        # Invalid reassignment (different record types)
+        (RecordSet({"model": ParametersRecord()}), "model", ConfigsRecord(), TypeError),
+    ],
+)
+def test_invalid_assignment(
+    rs: RecordSet, key: str, value: Any, exc_type: Type[Exception]
+) -> None:
+    """Test invalid assignment to RecordSet."""
+    with pytest.raises(exc_type):
+        rs[key] = value