diff --git a/SciLean/Lean/String.lean b/SciLean/Lean/String.lean
new file mode 100644
index 00000000..392a1e0f
--- /dev/null
+++ b/SciLean/Lean/String.lean
@@ -0,0 +1,16 @@
+
+
+/-- Split a string into substrings that have maximum size in bytes
+-/
+partial def String.splitToByteChunks (str : String) (chunkByteSize : Nat) : Array Substring := Id.run do
+  let mut chunks := #[]
+  let mut s : String.Pos := 0
+  let e : String.Pos := str.endPos
+  while s < e do
+    let mut s' := s
+    while (str.next s' - s).byteIdx ≤ chunkByteSize && s' < e do
+      s' := str.next s'
+    chunks := chunks.push (Substring.mk str s s')
+    s := s'
+  chunks
+