diff --git a/README.md b/README.md
index ce87da5..08b7919 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,69 @@ Some checks can be disabled in the `/etc/evocheck.cf` config file.
 
 Tests can be run with Vagrant and the provided `VagrantFile`.
 
+## How to contribute
+
+Read the CONTRIBUTING.md file.
+
+Try to respect the following conventions.
+
+### Use the verbose mode to explain errors
+
+The `failed` function takes a mandatory first argument for the check name and a secondary optional argument for the message to display in verbose mode. Example :
+
+```shell
+test -f /path/to/file || failed "IS_FILE_EXISTS" "Missing file \`/path/to/file'"
+```
+
+If the test is in a loop and might yield multiple errors, It's better to print a single error in normal mode and every error in verbose mode.
+
+```shell
+for user in $users; do
+    if ! groups "$user" | grep -q adm; then
+        failed "IS_USERINADMGROUP" "User $user doesn't belong to \`adm' group"
+        test "${VERBOSE}" = 1 || break
+    fi
+done
+```
+
+In a single check with multiple conditions, the verbose message helps determine which condition failed. Example :
+
+```shell
+if [ "$last_upgrade" -eq 0 ]; then
+    [ "$install_date" -lt "$limit" ] && failed "IS_NOTUPGRADED" "The system has never been updated"
+else
+    [ "$last_upgrade" -lt "$limit" ] && failed "IS_NOTUPGRADED" "The system hasn't been updated for too long"
+fi
+```
+
+### Use existing predicates
+
+There are a few predicate functions that help making conditionals.
+
+For Debian versions : `is_debian`, `is_debian_stretch`, `is_debian_jessie`…
+For packs : `is_pack_web`, `is_pack_samba`.
+For installed packages : `is_installed <package> [<package>]`.
+
+### Extact variables
+
+It's better not to inline function calls inside tests. Instead of this :
+
+```shell
+test "$(stat --format "%a" $MINIFW_FILE)" = "600" || failed "IS_MINIFWPERMS"
+```
+
+… prefer that :
+
+```shell
+actual=$(stat --format "%a" $MINIFW_FILE)
+expected="600"
+test "$expected" = "$actual" || failed "IS_MINIFWPERMS"
+```
+
+### Verify assumptions
+
+It's better to verify that a file, a directory or a command is present before using it, even if it's true in more than 99% of situations.
+
 ## How to build the package for a new Debian release
 
 On the master branch, add the last stable version with a release tag.