diff --git a/src/global.d.ts b/src/global.d.ts
index 668028f..7c00502 100644
--- a/src/global.d.ts
+++ b/src/global.d.ts
@@ -17,8 +17,8 @@ type TreeNode = {
   sha?: string
   accessDenied?: boolean
   comments?: {
-    active: number,
-    resolved: number,
+    active: number
+    resolved: number
   }
   diff?: {
     status: 'modified' | 'added' | 'removed' | 'renamed'
@@ -43,3 +43,10 @@ type VoidFN<T> = (payload: T) => void
 
 type Async<T> = T | Promise<T>
 type EnumString<S extends string> = S | (string & {})
+
+type JSONPrimitive = string | number | boolean | null | undefined
+type JSONObject = {
+  [key: string]: JSONValue
+}
+type JSONArray = JSONValue[]
+type JSONValue = JSONPrimitive | JSONObject | JSONArray
diff --git a/src/utils/is.ts b/src/utils/is.ts
new file mode 100644
index 0000000..b2ad89d
--- /dev/null
+++ b/src/utils/is.ts
@@ -0,0 +1,16 @@
+export const is = {
+  boolean: (d: unknown): d is boolean => typeof d === 'boolean',
+  number: (d: unknown): d is number => typeof d === 'number',
+  string: (d: unknown): d is string => typeof d === 'string',
+  JSON: {
+    object(d: unknown): d is JSONObject {
+      return (typeof d === 'object' && d && !Array.isArray(d)) || false
+    },
+    array(d: unknown): d is JSONArray {
+      return Array.isArray(d)
+    },
+    plain(d: unknown): d is JSONPrimitive {
+      return d === null || d === 'undefined' || is.boolean(d) || is.number(d) || is.string(d)
+    },
+  },
+}