diff --git a/by_json/README.md b/by_json/README.md
index d593134..d90a476 100644
--- a/by_json/README.md
+++ b/by_json/README.md
@@ -11,11 +11,10 @@
 
 # Usage
 
-  * Open **commons.sh** file
   * change **RERO\_DIR** variable to point your **rero-ils directory**
 
 ```
-make clean && make
+make clean && RERO_DIR="/home/moi/rero/rero-ils" make
 ```
 
 Result: **2 files (orgas.svg and policies.svg)** file (can be open with Gimp for example).
diff --git a/by_json/commons.sh b/by_json/commons.sh
index f177875..e040a96 100644
--- a/by_json/commons.sh
+++ b/by_json/commons.sh
@@ -5,6 +5,7 @@
 
 # Built variables
 outputfile="$1"
+RERO_DIR="${RERO_DIR:-${HOME}/projets/rero/rero-ils}"
 SRC_DIR="${RERO_DIR}/data/"
 
 # Templates
@@ -32,6 +33,14 @@ elif [[ -f "${outputfile}" ]]; then
   echo "File already exists!"
   exit 1
 fi
+if [[ ! -d "${RERO_DIR}" ]]; then
+  echo "Source directory doesn't exist: ${RERO_DIR}. Did you set RERO_DIR variable?"
+  exit 1
+fi
+if [[ ! -d "${SRC_DIR}" ]]; then
+  echo "No data directory found in ${RERO_DIR}. Did you set RERO_DIR variable correctly?"
+  exit 1
+fi
 
 # FUNCTIONS
 # WRITE first argument in output file
diff --git a/by_json/gen_orgas.sh b/by_json/gen_orgas.sh
index a206643..0ee8df0 100755
--- a/by_json/gen_orgas.sh
+++ b/by_json/gen_orgas.sh
@@ -10,9 +10,6 @@
 #    dot -Tsvg output.dot -o organisations.svg
 # where `output.dot` is the previous file. And `organisations.svg` the final schema you want to display.
 
-# CONFIG
-RERO_DIR="${HOME}/projets/rero/rero-ils"
-
 # Load commons variables, functions and statements
 source commons.sh
 
diff --git a/by_json/gen_policies.sh b/by_json/gen_policies.sh
index d20d3d5..292e5c5 100755
--- a/by_json/gen_policies.sh
+++ b/by_json/gen_policies.sh
@@ -3,9 +3,6 @@
 # Generate a dot file to create graph of RERO-ils data
 #
 
-# CONFIG
-RERO_DIR="${HOME}/projets/rero/rero-ils"
-
 # Load commons variables, functions and statements
 source commons.sh