diff --git a/searx/engines/elasticsearch.py b/searx/engines/elasticsearch.py
index c721114a7..58b5ba3cc 100644
--- a/searx/engines/elasticsearch.py
+++ b/searx/engines/elasticsearch.py
@@ -135,14 +135,38 @@ def _terms_query(query):
 
 
 def _custom_query(query):
-    key, value = query.split(':')
-    custom_query = custom_query_json
+    key = value = None
+    if any(placeholder in custom_query_json for placeholder in ["{{KEY}}", "{{VALUE}}", "{{VALUES}}"]):
+        try:
+            key, value = query.split(':', maxsplit=1)
+        except Exception as e:
+            raise ValueError('query format must be "key:value"') from e
+        if not key:
+            raise ValueError('empty key from "key:value" query')
+    try:
+        custom_query = loads(custom_query_json)
+    except Exception as e:
+        raise ValueError('invalid custom_query string') from e
+    return _custom_query_r(query, key, value, custom_query)
+
+
+def _custom_query_r(query, key, value, custom_query):
+    new_query = {}
     for query_key, query_value in custom_query.items():
         if query_key == '{{KEY}}':
-            custom_query[key] = custom_query.pop(query_key)
-        if query_value == '{{VALUE}}':
-            custom_query[query_key] = value
-    return custom_query
+            query_key = key
+
+        if isinstance(query_value, dict):
+            query_value = _custom_query_r(query, key, value, query_value)
+        elif query_value == '{{VALUE}}':
+            query_value = value
+        elif query_value == '{{VALUES}}':
+            query_value = value.split(',')
+        elif query_value == '{{QUERY}}':
+            query_value = query
+
+        new_query[query_key] = query_value
+    return new_query
 
 
 def response(resp):
diff --git a/tests/unit/engines/test_elasticsearch.py b/tests/unit/engines/test_elasticsearch.py
new file mode 100644
index 000000000..9749a132c
--- /dev/null
+++ b/tests/unit/engines/test_elasticsearch.py
@@ -0,0 +1,136 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# pylint: disable=missing-module-docstring
+
+'''
+searx is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+searx is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with searx. If not, see < http://www.gnu.org/licenses/ >.
+
+'''
+
+from json import loads
+from searx.engines import elasticsearch as elasticsearch_engine
+from tests import SearxTestCase
+
+
+class TestElasticsearchEngine(SearxTestCase):  # pylint: disable=missing-class-docstring
+    default_params = {"headers": {}}
+
+    def test_url_settings(self):
+        elasticsearch_engine.base_url = 'http://es:12345'
+        elasticsearch_engine.index = 'index'
+        params = elasticsearch_engine.request("city:berlin", self.default_params)
+        self.assertEqual(params["url"], "http://es:12345/index/_search")
+
+    def test_basic_queries(self):
+        queries = [
+            ['match', 'field:stuff', '{"query": {"match": {"field": {"query": "stuff"}}}}'],
+            ['simple_query_string', 'stuff', '{"query": {"simple_query_string": {"query": "stuff"}}}'],
+            ['term', 'field:stuff', '{"query": {"term": {"field": "stuff"}}}'],
+            ['terms', 'field:stuff1,stuff2', '{"query": {"terms": {"field": ["stuff1", "stuff2"]}}}'],
+        ]
+
+        for query in queries:
+            elasticsearch_engine.query_type = query[0]
+            params = elasticsearch_engine.request(query[1], self.default_params)
+            self.assertEqual(loads(params["data"]), loads(query[2]))
+
+    def test_basic_failures(self):
+        queries = [
+            ['match', 'stuff', 'query format must be "key:value'],
+            ['term', 'stuff', 'query format must be key:value'],
+            ['terms', 'stuff', 'query format must be key:value1,value2'],
+        ]
+
+        for query in queries:
+            elasticsearch_engine.query_type = query[0]
+            with self.assertRaises(ValueError) as context:
+                elasticsearch_engine.request(query[1], self.default_params)
+            self.assertIn(query[2], str(context.exception))
+
+    def test_custom_queries(self):
+        queries = [
+            [
+                'field:stuff',
+                '{"query": {"match": {"{{KEY}}": {"query": "{{VALUE}}"}}}}',
+                '{"query": {"match": {"field": {"query": "stuff"}}}}',
+            ],
+            [
+                'stuff',
+                '{"query": {"simple_query_string": {"query": "{{QUERY}}"}}}',
+                '{"query": {"simple_query_string": {"query": "stuff"}}}',
+            ],
+            [
+                'space stuff',
+                '{"query": {"simple_query_string": {"query": "{{QUERY}}"}}}',
+                '{"query": {"simple_query_string": {"query": "space stuff"}}}',
+            ],
+            [
+                '"space stuff"',
+                '{"query": {"simple_query_string": {"query": "{{QUERY}}"}}}',
+                '{"query": {"simple_query_string": {"query": "\\\"space stuff\\\""}}}',
+            ],
+            [
+                "embedded'apostrophe",
+                '{"query": {"simple_query_string": {"query": "{{QUERY}}"}}}',
+                '{"query": {"simple_query_string": {"query": "embedded\'apostrophe"}}}',
+            ],
+            [
+                'more:stuff',
+                '{"query": {"simple_query_string": {"query": "{{QUERY}}"}}}',
+                '{"query": {"simple_query_string": {"query": "more:stuff"}}}',
+            ],
+            [
+                'field:stuff',
+                '{"query": {"term": {"{{KEY}}": "{{VALUE}}"}}}',
+                '{"query": {"term": {"field": "stuff"}}}',
+            ],
+            [
+                'field:more:stuff',
+                '{"query": {"match": {"{{KEY}}": {"query": "{{VALUE}}"}}}}',
+                '{"query": {"match": {"field": {"query": "more:stuff"}}}}',
+            ],
+            [
+                'field:stuff1,stuff2',
+                '{"query": {"terms": {"{{KEY}}": "{{VALUES}}"}}}',
+                '{"query": {"terms": {"field": ["stuff1", "stuff2"]}}}',
+            ],
+            [
+                'field:stuff1',
+                '{"query": {"terms": {"{{KEY}}": "{{VALUES}}"}}}',
+                '{"query": {"terms": {"field": ["stuff1"]}}}',
+            ],
+        ]
+
+        elasticsearch_engine.query_type = 'custom'
+        for query in queries:
+            elasticsearch_engine.custom_query_json = query[1]
+            params = elasticsearch_engine.request(query[0], self.default_params)
+            self.assertEqual(loads(params["data"]), loads(query[2]))
+
+    def test_custom_failures(self):
+        queries = [
+            ['stuff', '{"query": {"match": {"{{KEY}}": {"query": "{{VALUE}}"}}}}', 'query format must be "key:value"'],
+            ['stuff', '{"query": {"terms": {"{{KEY}}": "{{VALUES}}"}}}', 'query format must be "key:value"'],
+            ['stuff', '{"query": {"simple_query_string": {"query": {{QUERY}}}}}', 'invalid custom_query string'],
+            ['stuff', '"query": {"simple_query_string": {"query": "{{QUERY}}"}}}', 'invalid custom_query string'],
+        ]
+
+        elasticsearch_engine.query_type = 'custom'
+        for query in queries:
+            elasticsearch_engine.custom_query_json = query[1]
+            with self.assertRaises(ValueError) as context:
+                elasticsearch_engine.request(query[0], self.default_params)
+            self.assertIn(query[2], str(context.exception))
+
+
+# vi:sw=4