diff --git a/NOTICE b/NOTICE
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index e69de29..0000000
diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
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+# simple-cache
+
+A simple library for caching data.
+
+## Installation
+You can install the library using `pip`:
+
+```bash
+pip install simple-cache --index-url https://repo.jcloud-services.ddns.net/simple/
+```
+
+## Full documentation
+
+### `CacheItem`
+A cache item.
+
+#### Params
+- `value` (type: `Any`): The value of the item
+- `creation_time` (type: `Union[int, float]`): The time the item was created
+
+#### Exceptions
+
+No exceptions.
+
+#### Methods
+
+No methods.
+
+### `Cache`
+A thread-safe cache.
+
+#### Parameters
+- `generate_value_func` (type: `Optional[FunctionType]`, default: `None`): The function to generate a new value. It has to take one positional argument.
+- `max_size` (type: `int`, default: `256`): The maximum size of the cache.
+- `ttl` (type: `int`, default: `120`): The TTL (time to live) in seconds.
+
+#### Exceptions
+
+No exceptions.
+
+#### Methods
+
+##### `set`
+
+Sets or updates an item (thread-safe).
+
+###### Parameters
+
+- `key` (type: `str`): The key.
+- `value` (type: `Any`): The value.
+
+###### Exceptions
+
+No exceptions.
+
+###### Returns
+
+`None`
+
+##### `delete`
+Deletes an item (thread-safe).
+
+###### Parameters
+
+- `key` (type: `str`): The key.
+
+###### Exceptions
+
+- `KeyError`: If the item does not exist.
+
+###### Returns
+
+`None`
+
+##### `get`
+
+Returns an item (thread-safe).
+If the item does not exist, it uses ``self.generate_value_func`` to
+get the value. If no ``generate_value_func`` was specified in the
+constructor of the ``Cache`` object, the value will be set to ``None``.
+
+###### Parameters
+
+- `key` (type: `str`): The key.
+
+###### Exceptions
+
+No exceptions.
+
+###### Returns
+
+The value.
+Type: `Any`
+
+##### `clean_item`
+
+Removes an item if it is expired (thread-safe).
+
+###### Parameters
+
+- `key` (type: `key`): The key
+
+###### Exceptions
+
+No exceptions.
+
+###### Returns
+
+`None`
+
+##### `clear_expired`
+
+Removes all expired items (thread-safe).
+
+###### Parameters
+
+No parameters.
+
+###### Exceptions
+
+No Exceptions.
+
+###### Returns
+
+`None`
+
+##### `clear`
+
+Removes all items (thread-safe).
+
+###### Parameters
+
+No parameters.
+
+###### Exceptions
+
+No Exceptions.
+
+###### Returns
+
+`None`
+
+## Changelog
+
+### Version 0.1.0
+- initial release
+- thread safety
+- set, update, delete and get items
+- TTL
+- support for specifying a function to generate new values
+- deletion of expired items when getting them
+- deletion of the least used item when a new item is set and the maximum size is reached
+- support for clearing the cache
\ No newline at end of file
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..b21e2f9
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,9 @@
+[build-system]
+requires = ["setuptools", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "simple-cache"
+version = "0.1.0"
+description = "A simple library for caching data."
+license = "Apache-2.0"
\ No newline at end of file
diff --git a/src/simple_cache/__init__.py b/src/simple_cache/__init__.py
new file mode 100644
index 0000000..5e864b8
--- /dev/null
+++ b/src/simple_cache/__init__.py
@@ -0,0 +1,24 @@
+# Copyright 2026 jCloud Services GbR
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+'''
+A simple library for caching data.
+'''
+
+from ._core import *
+from ._core import __all__ as _core__all__
+
+__all__ = [
+    *_core__all__
+]
\ No newline at end of file
diff --git a/src/simple_cache/_core.py b/src/simple_cache/_core.py
new file mode 100644
index 0000000..6708159
--- /dev/null
+++ b/src/simple_cache/_core.py
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+from heapq import nsmallest
+import time
+import threading
+from types import FunctionType
+from typing import Optional, Any, Union
+
+__all__ = [
+    'CacheItem',
+    'Cache'
+]
+
+def _genval(_) -> None:
+    '''
+    The fallback function for the ``generate_value_func`` argument for the
+    constructor of ``Cache``. It simply returns ``None``, without performing any
+    additional operations.
+    '''
+    pass
+
+class CacheItem:
+    def __init__(self, value: Any, creation_time: Union[int, float]):
+        '''
+        A cache item.
+
+        :param value: The value of the item
+        :type value: Any
+        :param creation_time: The time the item was created
+        :type creation_time: Union[int, float]
+        '''
+
+        self.value = value
+        self.creation_time = creation_time
+
+class Cache:
+    def __init__(self, generate_value_func: Optional[FunctionType] = None, max_size: int = 256, ttl: int = 120):
+        '''
+        A thread-safe cache.
+        
+        :param generate_value_func: The function to generate a new value. It has to take one positional argument.
+        :type generate_value_func: Optional[FunctionType]
+        :param max_size: The maximum size of the cache.
+        :type max_size: int
+        :param ttl: The TTL (time to live) in seconds.
+        :type ttl: int
+        '''
+
+        if generate_value_func is None:
+            generate_value_func = _genval
+
+        self._cache = dict()
+        self.max_size = max_size
+        self.ttl = ttl
+        self.generate_value_func = generate_value_func
+        self._accesses = dict()
+        self._all_accesses = 0
+        self._lock = threading.RLock()
+
+    def _get_least_used_keys(self, number_of_keys: int = 1) -> list:
+        '''
+        Returns the keys that are used the least. The number of keys that are
+        returned can be specified with the parameter ``number_of_keys``.
+        
+        :param number_of_keys: The number of keys to return.
+        :type number_of_keys: int
+        
+        :return: The ``number_of_keys``-th least used keys.
+        :rtype: list
+        '''
+
+        if not self._accesses or number_of_keys <= 0:
+            return []
+
+        return [k for k in nsmallest(number_of_keys, self._accesses, key = lambda k: self._accesses[k])]
+
+    def _set(self, key: str, value: Any) -> None:
+        '''
+        Sets or updated an item.
+
+        :param key: The key.
+        :type key: str
+        :param value: The value.
+        :type value: Any
+        '''
+
+        new_key = key not in self._cache.keys()
+        if len(self._cache) >= self.max_size and new_key:
+            self._clear_expired()
+            if len(self._cache) >= self.max_size:
+                least_used_keys = self._get_least_used_keys(1)
+                if least_used_keys:
+                    self._delete(least_used_keys[0])
+
+        self._accesses[key] = 0 if new_key else self._accesses[key]
+        self._cache[key] = CacheItem(value, time.time())
+
+    def _delete(self, key: str) -> None:
+        '''
+        Deletes an item.
+        
+        :param key: The key.
+        :type key: str
+
+        :raises KeyError: If the item does not exist.
+        '''
+
+        if key in self._cache:
+            self._all_accesses -= self._accesses[key]
+            del self._cache[key]
+            del self._accesses[key]
+        else:
+            raise KeyError(key)
+
+    def _get(self, key: str) -> Any:
+        '''
+        Returns an item.
+        If the item does not exist, it uses ``self.generate_value_func`` to
+        get the value. If no ``generate_value_func`` was specified in the
+        constructor of the ``Cache`` object, the value will be set to ``None``.
+
+        :param key: The key.
+        :type key: str
+
+        :return: The value.
+        :rtype: Any
+        '''
+
+        self._clean_item(key)
+        if key in self._cache:
+            value = self._cache[key].value
+        else:
+            value = self.generate_value_func(key)
+            self._set(key, value)
+        self._accesses[key] += 1
+        self._all_accesses += 1
+        return value
+
+    def _clean_item(self, key: str) -> None:
+        '''
+        Removes an item if it is expired.
+
+        :param key: The key.
+        :type key: str
+        '''
+
+        if key in self._cache:
+            ct = self._cache[key].creation_time 
+            if time.time() - ct > self.ttl:
+                self._delete(key)
+
+    def _clear_expired(self) -> None:
+        '''
+        Removes all expired items.
+        '''
+
+        expired = [k for k, v in self._cache.items() if time.time() - v.creation_time > self.ttl]
+        for e in expired:
+            self._delete(e)
+
+    def _clear(self) -> None:
+        '''
+        Removes all items.
+        '''
+
+        self._all_accesses = 0
+        self._accesses = dict()
+        self._cache = dict()
+
+    def set(self, key: str, value: Any) -> None:
+        '''
+        Sets or updates an item (thread-safe).
+
+        :param key: The key.
+        :type key: str
+        :param value: The value.
+        :type value: Any
+        '''
+
+        with self._lock:
+            self._set(key, value)
+
+    def delete(self, key: str) -> None:
+        '''
+        Deletes an item (thread-safe).
+        
+        :param key: The key.
+        :type key: str
+
+        :raises KeyError: If the item does not exist.
+        '''
+        with self._lock:
+            self._delete(key)
+
+    def get(self, key: str) -> Any:
+        '''
+        Returns an item (thread-safe).
+        If the item does not exist, it uses ``self.generate_value_func`` to
+        get the value. If no ``generate_value_func`` was specified in the
+        constructor of the ``Cache`` object, the value will be set to ``None``.
+
+        :param key: The key.
+        :type key: str
+
+        :return: The value.
+        :rtype: Any
+        '''
+
+        with self._lock:
+            return self._get(key)
+
+    def clean_item(self, key: str) -> None:
+        '''
+        Removes an item if it is expired (thread-safe).
+
+        :param key: The key.
+        :type key: str
+        '''
+
+        with self._lock:
+            self._clean_item(key)
+
+    def clear_expired(self) -> None:
+        '''
+        Removes all expired items (thread-safe).
+        '''
+
+        with self._lock:
+            self._clear_expired()
+
+    def clear(self) -> None:
+        '''
+        Removes all items (thread-safe).
+        '''
+
+        with self._lock:
+            self._clear()
+
+    def __getitem__(self, key: str) -> Any:
+        return self.get(key)
+    
+    def __setitem__(self, key: str, value: Any) -> None:
+        self.set(key, value)
+
+    def __delitem__(self, key: str) -> None:
+        self.delete(key)
\ No newline at end of file