diff --git a/src/jira_hub/commands.py b/src/jira_hub/commands.py
index f44a249..a1752fc 100644
--- a/src/jira_hub/commands.py
+++ b/src/jira_hub/commands.py
@@ -22,6 +22,8 @@ SPEC = {
     "refresh": {"required": [], "optional": ["keys", "jql"], "keys": ["keys"]},
 }
 WRITE_TYPES = [t for t in SPEC if t != "refresh"]
+LIST_PARAMS = {"labels", "labels_add", "labels_remove", "keys"}
+BOOL_PARAMS = {"replace"}
 
 
 class CommandError(ValueError):
@@ -49,6 +51,23 @@ def temp_keys_used(cmd) -> list[str]:
     return [k for k in referenced_keys(cmd) if is_temp(k) and k != own]
 
 
+def _type_error(ctype, name, value) -> str | None:
+    """Проверка типа значения параметра (M-3 #12): иначе .strip() и подстановка ключей падают с 500.
+    null допустим везде — обязательность проверяется отдельно."""
+    if value is None:
+        return None
+    if name in LIST_PARAMS:
+        ok, want = isinstance(value, list) and all(isinstance(v, str) for v in value), "список строк"
+    elif name in BOOL_PARAMS:
+        ok, want = isinstance(value, bool), "true или false"
+    elif ctype == "ensure_status" and name == "target":
+        ok = isinstance(value, str) or (isinstance(value, list) and all(isinstance(v, str) for v in value))
+        want = "строка или список строк"
+    else:
+        ok, want = isinstance(value, str), "строка"
+    return None if ok else f"{name} — {want}"
+
+
 def validate(commands) -> list[dict]:
     if not isinstance(commands, list) or not commands:
         raise CommandError("пакет без команд")
@@ -68,6 +87,9 @@ def validate(commands) -> list[dict]:
         unknown = set(params) - set(spec["required"]) - set(spec["optional"])
         if unknown:
             raise CommandError(f"команда {i} ({ctype}): лишние параметры {', '.join(sorted(unknown))}")
+        bad = [e for e in (_type_error(ctype, n, v) for n, v in params.items()) if e]
+        if bad:
+            raise CommandError(f"команда {i} ({ctype}): " + "; ".join(bad))
         if ctype == "ensure_fields" and not any(f in params for f in spec["optional"]):
             raise CommandError(f"команда {i}: ensure_fields без полей")
         if ctype == "refresh" and not (params.get("keys") or params.get("jql")):
diff --git a/tests/test_commands.py b/tests/test_commands.py
index 9e42b2f..daae8eb 100644
--- a/tests/test_commands.py
+++ b/tests/test_commands.py
@@ -123,3 +123,29 @@ def test_validate_rejects_duplicate_issue_summary():
         commands.validate(cmds)
     assert "повторяется тема ensure_issue: «Отчёт»" in str(e.value)
     commands.validate([cmds[0], cmds[2]])                                # регистр различается — пакет допустим
+
+
+@pytest.mark.parametrize("cmd, name", [
+    ({"type": "ensure_issue", "params": {"temp_key": "new:1", "issue_type": "task", "summary": 42}}, "summary"),
+    ({"type": "ensure_fields", "params": {"key": "A-1", "labels_add": "AWPCA"}}, "labels_add"),
+    ({"type": "ensure_fields", "params": {"key": "A-1", "labels_remove": ["x", 1]}}, "labels_remove"),
+    ({"type": "ensure_fields", "params": {"key": ["A-1"], "duedate": "2026-10-23"}}, "key"),
+    ({"type": "ensure_comment", "params": {"key": "A-1", "marker": "m", "body": {"t": 1}}}, "body"),
+    ({"type": "ensure_status", "params": {"key": "A-1", "target": 5}}, "target"),
+    ({"type": "ensure_status", "params": {"key": "A-1", "target": ["Разработка", 2]}}, "target"),
+    ({"type": "ensure_link", "params": {"source": "A-1", "target": "A-2", "link_type": "связанные", "replace": "да"}}, "replace"),
+    ({"type": "refresh", "params": {"keys": "A-1"}}, "keys"),
+])
+def test_validate_rejects_wrong_types(cmd, name):
+    with pytest.raises(commands.CommandError) as e:
+        commands.validate([cmd])
+    assert name in str(e.value)
+
+
+def test_validate_accepts_null_for_clearable_and_path_target():
+    out = commands.validate([
+        {"type": "ensure_fields", "params": {"key": "A-1", "assignee": None, "epic_key": None, "duedate": None}},
+        {"type": "ensure_status", "params": {"key": "A-1", "target": ["Разработка", "Готово"]}},
+        {"type": "ensure_link", "params": {"source": "A-1", "target": "A-2", "link_type": "связанные", "replace": True}},
+    ])
+    assert len(out) == 3