diff --git a/docs/modules/json.md b/docs/modules/json.md
index 056d02eb..e1dc9853 100644
--- a/docs/modules/json.md
+++ b/docs/modules/json.md
@@ -3,14 +3,17 @@ icon: package
 label: json
 ---
 
+pkpy has two JSON modules.
+1. The built-in JSON module is always available and can be imported via `import json`.
+2. After `v1.2.7`, you can set `PK_USE_CJSON` to `ON` in CMakeLists.txt to enable an alternative JSON module `cjson`.
+
+Their interfaces are the same, `cjson` is faster while the built-in `json` is more stable since it was developed earlier.
+
 ### `json.loads(s)`
 
 Decode a JSON string into a python object.
 
-It is supported by the `eval()` function.
-
 ### `json.dumps(obj)`
 
 Encode a python object into a JSON string.
 
-It is supported by the compiler with `JSON_MODE` enabled.