diff --git a/10.md b/10.md
index 8c2c436c..5a4a2034 100644
--- a/10.md
+++ b/10.md
@@ -67,6 +67,14 @@ Each individual tag is an array of **ONE or more strings**. The first element of
 `["locktime", 1765300829]` - a tag must contain **strings** only\
 `["locktime", ""]` - a tag must contain **non-empty strings** only
 
+## Witness
+
+Signatures or other witness data are provided in the `Proof.witness` as a serialized JSON string of the witness object for the NUT-10 kind.
+
+> [!IMPORTANT]
+> `Proof.witness` is only expected for proofs containing a NUT-10 Well-known Secret.
+> A mint MAY reject a Proof containing a witness field if its secret cannot be parsed as a [Well-known Secret](#well-known-secret)).
+
 ## Examples
 
 Example use cases of this secret format are