diff --git a/common/jinja/runtime.cpp b/common/jinja/runtime.cpp
index f234d9284f..4453d86e6d 100644
--- a/common/jinja/runtime.cpp
+++ b/common/jinja/runtime.cpp
@@ -144,6 +144,13 @@ value binary_expression::execute_impl(context & ctx) {
         return false;
     };
 
+    auto test_is_in = [&]() -> bool {
+        func_args args(ctx);
+        args.push_back(left_val);
+        args.push_back(right_val);
+        return global_builtins().at("test_is_in")(args)->as_bool();
+    };
+
     // Handle undefined and null values
     if (is_val<value_undefined>(left_val) || is_val<value_undefined>(right_val)) {
         if (is_val<value_undefined>(right_val) && (op.value == "in" || op.value == "not in")) {
@@ -223,19 +230,11 @@ value binary_expression::execute_impl(context & ctx) {
             return result;
         }
     } else if (is_val<value_array>(right_val)) {
-        auto & arr = right_val->as_array();
-        bool member = false;
-        for (const auto & item : arr) {
-            if (*left_val == *item) {
-                member = true;
-                break;
-            }
-        }
+        // case: 1 in [0, 1, 2]
+        bool member = test_is_in();
         if (op.value == "in") {
-            JJ_DEBUG("Checking membership: %s in Array is %d", left_val->type().c_str(), member);
             return mk_val<value_bool>(member);
         } else if (op.value == "not in") {
-            JJ_DEBUG("Checking non-membership: %s not in Array is %d", left_val->type().c_str(), !member);
             return mk_val<value_bool>(!member);
         }
     }
@@ -252,22 +251,23 @@ value binary_expression::execute_impl(context & ctx) {
 
     // String membership
     if (is_val<value_string>(left_val) && is_val<value_string>(right_val)) {
-        auto left_str = left_val->as_string().str();
-        auto right_str = right_val->as_string().str();
+        // case: "a" in "abc"
+        bool member = test_is_in();
         if (op.value == "in") {
-            return mk_val<value_bool>(right_str.find(left_str) != std::string::npos);
+            return mk_val<value_bool>(member);
         } else if (op.value == "not in") {
-            return mk_val<value_bool>(right_str.find(left_str) == std::string::npos);
+            return mk_val<value_bool>(!member);
         }
     }
 
     // Value key in object
     if (is_val<value_object>(right_val)) {
-        bool has_key = right_val->has_key(left_val);
+        // case: key in {key: value}
+        bool member = test_is_in();
         if (op.value == "in") {
-            return mk_val<value_bool>(has_key);
+            return mk_val<value_bool>(member);
         } else if (op.value == "not in") {
-            return mk_val<value_bool>(!has_key);
+            return mk_val<value_bool>(!member);
         }
     }
 
diff --git a/common/jinja/value.cpp b/common/jinja/value.cpp
index f254ae9251..2aa156b177 100644
--- a/common/jinja/value.cpp
+++ b/common/jinja/value.cpp
@@ -393,6 +393,33 @@ const func_builtins & global_builtins() {
         {"test_is_lt", test_compare_fn<value_compare_op::lt>},
         {"test_is_lessthan", test_compare_fn<value_compare_op::lt>},
         {"test_is_ne", test_compare_fn<value_compare_op::ne>},
+        {"test_is_in", [](const func_args & args) -> value {
+            args.ensure_count(2);
+            auto needle   = args.get_pos(0);
+            auto haystack = args.get_pos(1);
+            if (is_val<value_undefined>(haystack)) {
+                return mk_val<value_bool>(false);
+            }
+            if (is_val<value_array>(haystack)) {
+                for (const auto & item : haystack->as_array()) {
+                    if (*needle == *item) {
+                        return mk_val<value_bool>(true);
+                    }
+                }
+                return mk_val<value_bool>(false);
+            }
+            if (is_val<value_string>(haystack)) {
+                if (!is_val<value_string>(needle)) {
+                    throw raised_exception("'in' test expects args[1] as string when args[0] is string, got args[1] as " + needle->type());
+                }
+                return mk_val<value_bool>(
+                    haystack->as_string().str().find(needle->as_string().str()) != std::string::npos);
+            }
+            if (is_val<value_object>(haystack)) {
+                return mk_val<value_bool>(haystack->has_key(needle));
+            }
+            throw raised_exception("'in' test expects iterable as first argument, got " + haystack->type());
+        }},
         {"test_is_test", [](const func_args & args) -> value {
             args.ensure_vals<value_string>();
             auto & builtins = global_builtins();
diff --git a/tests/test-jinja.cpp b/tests/test-jinja.cpp
index f6114f1e2f..1f25c6ae71 100644
--- a/tests/test-jinja.cpp
+++ b/tests/test-jinja.cpp
@@ -189,12 +189,24 @@ static void test_conditionals(testing & t) {
         "negated"
     );
 
-    test_template(t, "in operator",
+    test_template(t, "in operator (element in array)",
         "{% if 'x' in items %}found{% endif %}",
         {{"items", json::array({"x", "y"})}},
         "found"
     );
 
+    test_template(t, "in operator (substring)",
+        "{% if 'bc' in 'abcd' %}found{% endif %}",
+        json::object(),
+        "found"
+    );
+
+    test_template(t, "in operator (object key)",
+        "{% if 'key' in obj %}found{% endif %}",
+        {{"obj", {{"key", 1}, {"other", 2}}}},
+        "found"
+    );
+
     test_template(t, "is defined",
         "{% if x is defined %}yes{% else %}no{% endif %}",
         {{"x", 1}},
@@ -1036,6 +1048,42 @@ static void test_tests(testing & t) {
         json::object(),
         "yes"
     );
+
+    test_template(t, "is in (array, true)",
+        "{{ 'yes' if 2 is in([1, 2, 3]) }}",
+        json::object(),
+        "yes"
+    );
+
+    test_template(t, "is in (array, false)",
+        "{{ 'yes' if 5 is in([1, 2, 3]) else 'no' }}",
+        json::object(),
+        "no"
+    );
+
+    test_template(t, "is in (string)",
+        "{{ 'yes' if 'bc' is in('abcde') }}",
+        json::object(),
+        "yes"
+    );
+
+    test_template(t, "is in (object keys)",
+        "{{ 'yes' if 'a' is in(obj) }}",
+        {{"obj", {{"a", 1}, {"b", 2}}}},
+        "yes"
+    );
+
+    test_template(t, "reject with in test",
+        "{{ items | reject('in', skip) | join(', ') }}",
+        {{"items", json::array({"a", "b", "c", "d"})}, {"skip", json::array({"b", "d"})}},
+        "a, c"
+    );
+
+    test_template(t, "select with in test",
+        "{{ items | select('in', keep) | join(', ') }}",
+        {{"items", json::array({"a", "b", "c", "d"})}, {"keep", json::array({"b", "c"})}},
+        "b, c"
+    );
 }
 
 static void test_string_methods(testing & t) {