diff --git a/README.md b/README.md
index 4489eb9..88c36cd 100644
--- a/README.md
+++ b/README.md
@@ -92,6 +92,7 @@ check if given string is valid
 | isbn | | verify ISBN code |
 | | .10 | check for ISBN-10 codes only |
 | | .13 | check for ISBN-13 codes only |
+| json | | test if string contains valid JSON |
 | url | | verify URL |
 
 ##### Returns