diff --git a/docs/source/external/matrix.rst b/docs/source/external/matrix.rst
new file mode 100644
index 0000000..22213a3
--- /dev/null
+++ b/docs/source/external/matrix.rst
@@ -0,0 +1,37 @@
+MATRIX
+======
+
+
+Post-processing grids
+---------------------
+
+We need to post-process the raw grids outputted by MATRIX -
+use one of the available interfaces (including the CLI) to do so.
+
+
+- **Optimize and scale:** apply the built-in optimization and rescaled by a factor if needed to go e.g. from pb to fb.
+
+- **Delete keys:** delete `y_label_unit`, `xlabel` and `x_label-tex`
+
+- **Add keys:**
+    .. list-table:: Additional keys
+        :widths: 25 25 50
+        :header-rows: 1
+
+        * - key
+          - value
+          - comment
+        * - y-unit
+          - pb/GeV
+          -
+        * - y-label
+          - differential x-sec
+          -
+        * - lumi_id_types
+          - pdg_mc_ids
+          - needed for compatibility with LHAPDF
+        * - arxiv
+          -
+          - put the original paper
+
+- **Add output log of MATRIX:** put the original MATRIX output log under the `results` key as usual
diff --git a/docs/source/index.rst b/docs/source/index.rst
index 4e1aceb..a6655ee 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -62,6 +62,7 @@ and the program will, if necessary, install the required external program and la
    external/index
    external/mg5
    external/yadism
+   external/matrix
    external/vrap
    external/pos
    external/int