diff --git a/conftest.py b/conftest.py
new file mode 100644
index 000000000..d29ed8113
--- /dev/null
+++ b/conftest.py
@@ -0,0 +1,3 @@
+import matplotlib as mpl
+
+mpl.use("Agg")
diff --git a/pyproject.toml b/pyproject.toml
index bec01e955..5f7d1956b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -39,6 +39,7 @@ classifiers = [
 dynamic = [ "version" ]
 dependencies = [
   "astropy>=6",
+  "lmfit>=1.2.2",
   "matplotlib>=3.7",
   "numpy>=1.24",
   "scikit-image>=0.21",
diff --git a/xrtpy/response/__init__.py b/xrtpy/response/__init__.py
index 1e863714d..09c577109 100644
--- a/xrtpy/response/__init__.py
+++ b/xrtpy/response/__init__.py
@@ -13,6 +13,8 @@
 from xrtpy.response.temperature_from_filter_ratio import temperature_from_filter_ratio
 from xrtpy.response.temperature_response import TemperatureResponseFundamental
 
+from . import tools
+
 __all__ = [
     "Geometry",
     "EntranceFilter",
@@ -24,4 +26,5 @@
     "EffectiveAreaFundamental",
     "TemperatureResponseFundamental",
     "temperature_from_filter_ratio",
+    "tools",
 ]