diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 7d2d6a8..2eaede8 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -24,7 +24,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: ['3.8', '3.9', '3.10', '3.11', '3.12']
+        python-version: ['3.9', '3.10', '3.11', '3.12']
 
     steps:
     - uses: actions/checkout@v3
diff --git a/docs/prompt.md b/docs/prompt.md
index 466b262..81b8b11 100644
--- a/docs/prompt.md
+++ b/docs/prompt.md
@@ -32,6 +32,11 @@ Banks supports the following ones, specific for prompt engineering.
     options:
         show_root_heading: false
 
+### `{{canary_word}}`
+
+Insert into the prompt a canary word that can be checked later with `Prompt.canary_leaked()`
+to ensure the original prompt was not leaked.
+
 ## Macros
 
 Macros are a way to implement complex logic in the template itself, think about defining functions but using Jinja
diff --git a/pyproject.toml b/pyproject.toml
index e7edecf..9a84997 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -7,7 +7,7 @@ name = "banks"
 dynamic = ["version"]
 description = 'A prompt programming language'
 readme = "README.md"
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 license = "MIT"
 keywords = []
 authors = [
@@ -16,7 +16,6 @@ authors = [
 classifiers = [
   "Development Status :: 4 - Beta",
   "Programming Language :: Python",
-  "Programming Language :: Python :: 3.8",
   "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
@@ -56,7 +55,7 @@ cov = [
 ]
 
 [[tool.hatch.envs.all.matrix]]
-python = ["3.8", "3.9", "3.10", "3.11", "3.12"]
+python = ["3.9", "3.10", "3.11", "3.12"]
 
 [tool.hatch.envs.lint]
 detached = false  # Normally the linting env can be detached, but mypy doesn't install all the stubs we need
diff --git a/src/banks/config.py b/src/banks/config.py
new file mode 100644
index 0000000..2547f41
--- /dev/null
+++ b/src/banks/config.py
@@ -0,0 +1,5 @@
+import os
+
+from .utils import strtobool
+
+async_enabled = strtobool(os.environ.get("BANKS_ASYNC_ENABLED", "false"))
diff --git a/src/banks/env.py b/src/banks/env.py
index 028e871..477210f 100644
--- a/src/banks/env.py
+++ b/src/banks/env.py
@@ -1,38 +1,28 @@
 # SPDX-FileCopyrightText: 2023-present Massimiliano Pippi <mpippi@gmail.com>
 #
 # SPDX-License-Identifier: MIT
-import os
-
 from jinja2 import Environment, select_autoescape
 
-from banks.extensions import GenerateExtension, HFInferenceEndpointsExtension
-from banks.filters import lemmatize
-from banks.loader import MultiLoader
+from .config import async_enabled
+from .filters import lemmatize
+from .loader import MultiLoader
 
 
-def strtobool(val: str) -> bool:
-    """Convert a string representation of truth to True or False.
+def _add_extensions(env):
+    """
+    We lazily add extensions so that we can use the env in the extensions themselves if needed.
 
-    True values are 'y', 'yes', 't', 'true', 'on', and '1'; false values
-    are 'n', 'no', 'f', 'false', 'off', and '0'.  Raises ValueError if
-    'val' is anything else.
+    For example, we use banks to manage the system prompt in `GenerateExtension`
     """
-    val = val.lower()
-    if val in ("y", "yes", "t", "true", "on", "1"):
-        return True
-    elif val in ("n", "no", "f", "false", "off", "0"):
-        return False
-    else:
-        msg = f"invalid truth value {val}"
-        raise ValueError(msg)
+    from .extensions import GenerateExtension, HFInferenceEndpointsExtension
 
+    env.add_extension(GenerateExtension)
+    env.add_extension(HFInferenceEndpointsExtension)
 
-async_enabled = strtobool(os.environ.get("BANKS_ASYNC_ENABLED", "false"))
 
 # Init the Jinja env
 env = Environment(
     loader=MultiLoader(),
-    extensions=[GenerateExtension, HFInferenceEndpointsExtension],
     autoescape=select_autoescape(
         enabled_extensions=("html", "xml"),
         default_for_string=False,
@@ -42,8 +32,9 @@ def strtobool(val: str) -> bool:
     enable_async=bool(async_enabled),
 )
 
-# Setup custom filters
+# Setup custom filters and default extensions
 env.filters["lemmatize"] = lemmatize
+_add_extensions(env)
 
 
 def with_env(cls):
diff --git a/src/banks/errors.py b/src/banks/errors.py
index f950d17..cf4c87b 100644
--- a/src/banks/errors.py
+++ b/src/banks/errors.py
@@ -7,3 +7,7 @@ class MissingDependencyError(Exception):
 
 class AsyncError(Exception):
     pass
+
+
+class CanaryWordError(Exception):
+    pass
diff --git a/src/banks/extensions/generate.py b/src/banks/extensions/generate.py
index 8275da8..c1a14c9 100644
--- a/src/banks/extensions/generate.py
+++ b/src/banks/extensions/generate.py
@@ -7,7 +7,11 @@
 from jinja2.ext import Extension
 from litellm import ModelResponse, acompletion, completion
 
+from banks.errors import CanaryWordError
+from banks.prompt import Prompt
+
 DEFAULT_MODEL = "gpt-3.5-turbo"
+SYSTEM_PROMPT = Prompt("{{canary_word}} You are a helpful assistant.")
 
 
 class GenerateExtension(Extension):
@@ -52,11 +56,14 @@ def _generate(self, text, model_name=DEFAULT_MODEL):
         To tweak the prompt used to generate content, change the variable `messages` .
         """
         messages = [
-            {"role": "system", "content": "You are a helpful assistant."},
+            {"role": "system", "content": SYSTEM_PROMPT.text()},
             {"role": "user", "content": text},
         ]
         response: ModelResponse = cast(ModelResponse, completion(model=model_name, messages=messages))
-        return response["choices"][0]["message"]["content"]
+        content: str = response["choices"][0]["message"]["content"]
+        if SYSTEM_PROMPT.canary_leaked(content):
+            msg = "The system prompt has leaked into the response, possible prompt injection!"
+            raise CanaryWordError(msg)
 
     async def _agenerate(self, text, model_name=DEFAULT_MODEL):
         """
@@ -65,7 +72,7 @@ async def _agenerate(self, text, model_name=DEFAULT_MODEL):
         To tweak the prompt used to generate content, change the variable `messages` .
         """
         messages = [
-            {"role": "system", "content": "You are a helpful assistant."},
+            {"role": "system", "content": SYSTEM_PROMPT.text()},
             {"role": "user", "content": text},
         ]
         response: ModelResponse = cast(ModelResponse, await acompletion(model=model_name, messages=messages))
diff --git a/src/banks/prompt.py b/src/banks/prompt.py
index 3930ac1..14974f0 100644
--- a/src/banks/prompt.py
+++ b/src/banks/prompt.py
@@ -3,13 +3,24 @@
 # SPDX-License-Identifier: MIT
 from typing import Optional
 
-from banks.env import async_enabled, env
-from banks.errors import AsyncError
+from .config import async_enabled
+from .env import env
+from .errors import AsyncError
+from .utils import generate_canary_word
 
 
 class BasePrompt:
-    def __init__(self, text: str) -> None:
+    def __init__(self, text: str, canary_word: Optional[str] = None) -> None:
         self._template = env.from_string(text)
+        self.defaults = {"canary_word": canary_word or generate_canary_word()}
+
+    def _get_context(self, data: Optional[dict]) -> dict:
+        if data is None:
+            return self.defaults
+        return data | self.defaults
+
+    def canary_leaked(self, text: str) -> bool:
+        return self.defaults["canary_word"] in text
 
     @classmethod
     def from_template(cls, name: str) -> "BasePrompt":
@@ -20,7 +31,7 @@ def from_template(cls, name: str) -> "BasePrompt":
 
 class Prompt(BasePrompt):
     def text(self, data: Optional[dict] = None) -> str:
-        data = data or {}
+        data = self._get_context(data)
         return self._template.render(data)
 
 
@@ -33,6 +44,6 @@ def __init__(self, text: str) -> None:
             raise AsyncError(msg)
 
     async def text(self, data: Optional[dict] = None) -> str:
-        data = data or {}
+        data = self._get_context(data)
         result: str = await self._template.render_async(data)
         return result
diff --git a/src/banks/utils.py b/src/banks/utils.py
new file mode 100644
index 0000000..48f17ef
--- /dev/null
+++ b/src/banks/utils.py
@@ -0,0 +1,23 @@
+import secrets
+
+
+def strtobool(val: str) -> bool:
+    """
+    Convert a string representation of truth to True or False.
+
+    True values are 'y', 'yes', 't', 'true', 'on', and '1'; false values
+    are 'n', 'no', 'f', 'false', 'off', and '0'.  Raises ValueError if
+    'val' is anything else.
+    """
+    val = val.lower()
+    if val in ("y", "yes", "t", "true", "on", "1"):
+        return True
+    elif val in ("n", "no", "f", "false", "off", "0"):
+        return False
+    else:
+        msg = f"invalid truth value {val}"
+        raise ValueError(msg)
+
+
+def generate_canary_word(prefix: str = "BANKS[", suffix: str = "]", token_length: int = 8) -> str:
+    return f"{prefix}{secrets.token_hex(token_length // 2)}{suffix}"
diff --git a/tests/__init__.py b/tests/__init__.py
index bd78f6a..0a47ebb 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1,3 +1,8 @@
 # SPDX-FileCopyrightText: 2023-present Massimiliano Pippi <mpippi@gmail.com>
 #
 # SPDX-License-Identifier: MIT
+import warnings
+
+# banks depends on modules producing loads of deprecation warnings, let's just ignore them,
+# nothing we can do anyways
+warnings.simplefilter("ignore", category=DeprecationWarning)
diff --git a/tests/test_prompt.py b/tests/test_prompt.py
new file mode 100644
index 0000000..c57ad07
--- /dev/null
+++ b/tests/test_prompt.py
@@ -0,0 +1,16 @@
+import regex as re
+
+from banks import Prompt
+
+
+def test_canary_word_generation():
+    p = Prompt("{{canary_word}}This is my prompt")
+    assert re.match(r"BANKS\[.{8}\]This is my prompt", p.text())
+
+
+def test_canary_word_leaked():
+    p = Prompt("{{canary_word}}This is my prompt")
+    assert p.canary_leaked(p.text())
+
+    p = Prompt("This is my prompt")
+    assert not p.canary_leaked(p.text())
diff --git a/tests/test_utils.py b/tests/test_utils.py
new file mode 100644
index 0000000..d3f9b32
--- /dev/null
+++ b/tests/test_utils.py
@@ -0,0 +1,47 @@
+import pytest
+import regex as re
+
+from banks.utils import generate_canary_word, strtobool
+
+
+def test_generate_canary_word_defaults():
+    default = generate_canary_word()
+    assert re.match(r"BANKS\[.{8}\]", default)
+
+
+def test_generate_canary_word_params():
+    only_token = generate_canary_word(prefix="", suffix="", token_length=16)
+    assert re.match(r".{16}", only_token)
+
+    only_prefix = generate_canary_word(prefix="foo", suffix="")
+    assert re.match(r"foo.{8}", only_prefix)
+
+    only_suffix = generate_canary_word(prefix="", suffix="foo")
+    assert re.match(r".{8}foo", only_suffix)
+
+
+def test_strtobool_error():
+    with pytest.raises(ValueError):
+        strtobool("42")
+
+
+@pytest.mark.parametrize(
+    "test_input,expected",
+    [
+        ("y", True),
+        ("yes", True),
+        ("t", True),
+        ("true", True),
+        ("on", True),
+        ("1", True),
+        ("n", False),
+        ("no", False),
+        ("f", False),
+        ("false", False),
+        ("off", False),
+        ("0", False),
+        pytest.param("42", True, marks=pytest.mark.xfail),
+    ],
+)
+def test_strtobool(test_input, expected):
+    assert strtobool(test_input) == expected