diff --git a/tests/test_edge_cases.py b/tests/test_edge_cases.py
new file mode 100644
index 0000000..a33a098
--- /dev/null
+++ b/tests/test_edge_cases.py
@@ -0,0 +1,182 @@
+"""Edge-case and validation tests for fields, queries, responses, and client."""
+
+from datetime import datetime
+from unittest.mock import Mock
+
+import pytest
+import requests_mock
+
+from leakix import (
+    AgeField,
+    Client,
+    CountryField,
+    CustomField,
+    ErrorResponse,
+    IPField,
+    MustQuery,
+    Operator,
+    PortField,
+    RawQuery,
+    Scope,
+    SuccessResponse,
+    TimeField,
+)
+
+
+class TestPortFieldEdgeCases:
+    @pytest.mark.parametrize(
+        "port",
+        [-1, -100, 65536, 70000, 100000],
+        ids=["neg-1", "neg-100", "65536", "70000", "100000"],
+    )
+    def test_invalid_ports(self, port):
+        with pytest.raises((ValueError, AssertionError)):
+            PortField(port)
+
+    @pytest.mark.parametrize(
+        "port",
+        [0, 1, 80, 443, 8080, 65535],
+        ids=["min", "one", "http", "https", "alt-http", "max"],
+    )
+    def test_valid_boundary_ports(self, port):
+        field = PortField(port)
+        assert field.serialize() == f"port:{port}"
+
+
+class TestCustomFieldEdgeCases:
+    def test_empty_string_value(self):
+        field = CustomField("", "test_field")
+        assert field.serialize() == "test_field:"
+
+    def test_empty_string_field_name(self):
+        field = CustomField("value", "")
+        assert field.serialize() == ":value"
+
+    def test_special_characters_in_value(self):
+        field = CustomField("test value with spaces", "field")
+        assert field.serialize() == "field:test value with spaces"
+
+
+class TestCountryFieldEdgeCases:
+    def test_empty_string(self):
+        field = CountryField("")
+        assert field.serialize() == "country:"
+
+    def test_single_char(self):
+        field = CountryField("X")
+        assert field.serialize() == "country:X"
+
+
+class TestIPFieldEdgeCases:
+    def test_empty_string(self):
+        field = IPField("")
+        assert field.serialize() == "ip:"
+
+    def test_ipv6_format(self):
+        field = IPField("::1")
+        assert field.serialize() == "ip:::1"
+
+
+class TestAgeFieldEdgeCases:
+    def test_zero_age(self):
+        field = AgeField(0)
+        assert field.serialize() == "age:0"
+
+    def test_negative_age(self):
+        field = AgeField(-1)
+        assert field.serialize() == "age:-1"
+
+    def test_large_age(self):
+        field = AgeField(999999)
+        assert field.serialize() == "age:999999"
+
+
+class TestTimeFieldEdgeCases:
+    def test_epoch_date(self):
+        field = TimeField(datetime(1970, 1, 1))
+        assert field.serialize() == 'time:"1970-01-01"'
+
+
+class TestQueryEdgeCases:
+    def test_raw_query_empty_string(self):
+        query = RawQuery("")
+        assert query.serialize() == ""
+
+    def test_raw_query_special_chars(self):
+        query = RawQuery('+host:*.example.com -port:"22"')
+        assert query.serialize() == '+host:*.example.com -port:"22"'
+
+    def test_must_query_with_all_operators(self):
+        for op in Operator:
+            field = CustomField("val", "f", op)
+            query = MustQuery(field)
+            result = query.serialize()
+            assert result.startswith("+")
+
+
+class TestClientEdgeCases:
+    def test_none_api_key(self):
+        client = Client(api_key=None)
+        assert "api-key" not in client.headers
+
+    def test_empty_string_api_key(self):
+        client = Client(api_key="")
+        assert "api-key" not in client.headers
+
+    def test_none_base_url_uses_default(self):
+        client = Client(base_url=None)
+        assert client.base_url == "https://leakix.net"
+
+    def test_empty_base_url_uses_default(self):
+        client = Client(base_url="")
+        assert client.base_url == "https://leakix.net"
+
+    def test_get_with_none_queries(self):
+        client = Client()
+        with requests_mock.Mocker() as m:
+            m.get(f"{client.base_url}/search", json=[], status_code=200)
+            response = client.get(Scope.SERVICE, queries=None)
+            assert response.is_success()
+            assert m.last_request.qs["q"] == ["*"]
+
+    def test_get_with_empty_query_list(self):
+        client = Client()
+        with requests_mock.Mocker() as m:
+            m.get(f"{client.base_url}/search", json=[], status_code=200)
+            response = client.get(Scope.SERVICE, queries=[])
+            assert response.is_success()
+            assert m.last_request.qs["q"] == ["*"]
+
+    def test_get_page_zero(self):
+        client = Client()
+        with requests_mock.Mocker() as m:
+            m.get(f"{client.base_url}/search", json=[], status_code=200)
+            response = client.get(Scope.SERVICE, page=0)
+            assert response.is_success()
+
+    def test_get_negative_page(self):
+        client = Client()
+        with pytest.raises(ValueError):
+            client.get(Scope.SERVICE, page=-1)
+
+
+class TestResponseEdgeCases:
+    def test_success_with_none_json(self):
+        mock = Mock()
+        mock.status_code = 200
+        mock.json.return_value = None
+        response = SuccessResponse(mock)
+        assert response.json() is None
+
+    def test_success_with_empty_list(self):
+        mock = Mock()
+        mock.status_code = 200
+        response = SuccessResponse(mock, response_json=[])
+        assert response.json() == []
+
+    def test_error_with_custom_status_code(self):
+        mock = Mock()
+        mock.status_code = 503
+        mock.json.return_value = {"error": "unavailable"}
+        response = ErrorResponse(mock, status_code=503)
+        assert response.status_code() == 503