diff --git a/python/_project.pyx b/python/_project.pyx
index 3ccf7ad..ae5b4b9 100644
--- a/python/_project.pyx
+++ b/python/_project.pyx
@@ -808,7 +808,25 @@ def spherical_projection(int Nside,
                          npx.ndarray[DTYPE_t, ndim=3] density not None,
                          DTYPE_t min_distance,
                          DTYPE_t max_distance, int progress=1, int integrator_id=0, DTYPE_t[:] shifter = None, int booster=-1):
-                         
+    """
+    spherical_projection(Nside, density, min_distance, max_distance, progress=1, integrator_id=0, shifter=None, booster=-1)
+    
+    Keyword arguments:
+      progress (int): show progress if it is equal to 1
+      integrator_id (int): specify the order of integration along the line of shift
+      shifter (DTYPE_t array): this is an array of size 3. It specifies the amount of shift to apply to the center, in unit of voxel
+      booster (int): what is the frequency of refreshment of the progress bar. Small number decreases performance by locking the GIL.
+      
+
+    Arguments:
+      Nside (int): Nside of the returned map
+      density (NxNxN array): this is the density field, expressed as a cubic array
+      min_distance (float): lower bound of the integration
+      max_distance (float): upper bound of the integration
+      
+    Returns:
+      an healpix map, as a 1-dimensional array.
+    """
     import healpy as hp
     import progressbar as pb
     cdef int i