diff --git a/src/dualentry_cli/output.py b/src/dualentry_cli/output.py
index bff4acd..c9c254d 100644
--- a/src/dualentry_cli/output.py
+++ b/src/dualentry_cli/output.py
@@ -85,12 +85,25 @@ def _print_list(data: dict, resource: str) -> None:
         console.print(f"\n[dim]Showing {len(items)} of {data['count']}[/dim]")
 
 
+def _warn_truncated_lines(record: dict) -> None:
+    if not record.get("has_more_lines"):
+        return
+    shown = len(record.get("items") or [])
+    total = record.get("lines_count")
+    if isinstance(total, int) and total > shown:
+        msg = f"Warning: showing {shown} of {total} lines. The API caps inline lines at 100."
+    else:
+        msg = f"Warning: showing {shown} lines. The API omitted the rest."
+    console.print(f"\n[yellow]{msg}[/yellow]")
+
+
 def _print_detail(data: dict, resource: str) -> None:
     detail_fn = _FORMATTERS.get(resource, (None, None))[1]
     if detail_fn:
         detail_fn(data)
     else:
         _print_generic_detail(data)
+    _warn_truncated_lines(data)
 
 
 # ── Shared: Transaction list (records with #, Date, Counterparty, Amount) ──
diff --git a/tests/test_output.py b/tests/test_output.py
index 1d4fb1a..aa3b82d 100644
--- a/tests/test_output.py
+++ b/tests/test_output.py
@@ -26,3 +26,95 @@ def test_table_format_single_item(self, capsys):
         format_output(data, fmt="table")
         captured = capsys.readouterr()
         assert "INV-001" in captured.out
+
+
+class TestTruncatedLinesWarning:
+    def _je(self, *, has_more_lines: bool, lines_count: int | None, n_items: int = 2) -> dict:
+        items = [
+            {
+                "account_name": f"Account {i}",
+                "memo": f"Line {i}",
+                "debit": "10.00" if i % 2 else "0.00",
+                "credit": "0.00" if i % 2 else "10.00",
+            }
+            for i in range(1, n_items + 1)
+        ]
+        record = {
+            "internal_id": 3,
+            "date": "2026-01-15",
+            "company_name": "Acme",
+            "currency_iso_4217_code": "USD",
+            "record_status": "posted",
+            "memo": "Payroll",
+            "items": items,
+            "has_more_lines": has_more_lines,
+        }
+        if lines_count is not None:
+            record["lines_count"] = lines_count
+        return record
+
+    def test_warns_when_has_more_lines(self, capsys):
+        from dualentry_cli.output import format_output
+
+        format_output(self._je(has_more_lines=True, lines_count=250, n_items=100), resource="journal-entry")
+        captured = capsys.readouterr()
+        assert "JOURNAL ENTRY" in captured.out
+        assert "Account 1" in captured.out
+        assert "Warning: showing 100 of 250 lines. The API caps inline lines at 100." in captured.out
+        assert captured.out.index("Account 1") < captured.out.index("Warning:")
+
+    def test_no_warn_when_complete(self, capsys):
+        from dualentry_cli.output import format_output
+
+        format_output(self._je(has_more_lines=False, lines_count=2), resource="journal-entry")
+        captured = capsys.readouterr()
+        assert "JOURNAL ENTRY" in captured.out
+        assert "Warning:" not in captured.out
+
+    def test_no_warn_when_flag_absent(self, capsys):
+        from dualentry_cli.output import format_output
+
+        record = self._je(has_more_lines=False, lines_count=2)
+        del record["has_more_lines"]
+        del record["lines_count"]
+        format_output(record, resource="journal-entry")
+        captured = capsys.readouterr()
+        assert "Warning:" not in captured.out
+
+    def test_fallback_without_lines_count(self, capsys):
+        from dualentry_cli.output import format_output
+
+        format_output(self._je(has_more_lines=True, lines_count=None), resource="journal-entry")
+        captured = capsys.readouterr()
+        assert "Warning: showing 2 lines. The API omitted the rest." in captured.out
+
+    def test_invoice_detail_also_warns(self, capsys):
+        from dualentry_cli.output import format_output
+
+        data = {
+            "internal_id": 1,
+            "number": "INV-001",
+            "date": "2026-01-15",
+            "company_name": "Acme",
+            "customer_name": "Buyer",
+            "currency_iso_4217_code": "USD",
+            "amount": "100.00",
+            "items": [{"memo": "Widget", "quantity": "1", "rate": "100.00"}],
+            "has_more_lines": True,
+            "lines_count": 150,
+        }
+        format_output(data, resource="invoice")
+        captured = capsys.readouterr()
+        assert "Warning: showing 1 of 150 lines. The API caps inline lines at 100." in captured.out
+
+    def test_json_keeps_flags_and_skips_warning(self, capsys):
+        from dualentry_cli.output import format_output
+
+        data = self._je(has_more_lines=True, lines_count=250, n_items=2)
+        format_output(data, resource="journal-entry", fmt="json")
+        captured = capsys.readouterr()
+        payload = json.loads(captured.out)
+        assert payload["has_more_lines"] is True
+        assert payload["lines_count"] == 250
+        assert "Warning:" not in captured.out
+        assert captured.err == ""