diff --git a/docs/DESIGN.mcp.md b/docs/DESIGN.mcp.md
index 7594e9a6448957bc90378fe161fc10c04009e1ac..7e2b280cda9d6442cfed1aec4d785f88ce9d4f85 100644
--- a/docs/DESIGN.mcp.md
+++ b/docs/DESIGN.mcp.md
@@ -250,7 +250,7 @@ |---|---|---|
 | `list_databases` | — | every database the caller may list: owner, name, visibility, description, default branch, head hash + commit time, `is_beads` |
 | `list_branches` | db | branches with head hashes |
 | `list_tables` | db, ref? | table names, columns (name/type/pk/nullable), row counts |
-| `read_rows` | db, table, ref?, offset?, limit? | a page of rows as strings, plus the table total |
+| `read_rows` | db, table, ref?, offset?, limit? | a page of rows as strings-or-null (a cell holding no value is JSON `null`, so a real NULL is not the string `"NULL"`), plus the table total |
 | `get_commit_log` | db, ref?, from?, limit? | commits: hash, author, date, message, parents |
 | `get_commit_diff` | db, hash | the per-table summary `browse.CommitSummary` computes |