diff --git a/tests/test_tools.py b/tests/test_tools.py
new file mode 100644
index 0000000..e2142d2
--- /dev/null
+++ b/tests/test_tools.py
@@ -0,0 +1,83 @@
+import pytest
+from devterm.tools.json_tool import format_json, validate_json
+from devterm.tools.jwt_tool import decode_jwt
+from devterm.tools.cron_tool import validate_cron, get_next_run
+from devterm.tools.base64_tool import encode_base64, decode_base64
+from devterm.tools.url_tool import encode_url, decode_url
+
+
+class TestJsonTool:
+    def test_format_json(self):
+        result = format_json('{"key":"value"}')
+        assert '{\n  "key": "value"\n}' == result
+
+    def test_format_nested_json(self):
+        result = format_json('{"a":{"b":{"c":1}}}')
+        assert '"c": 1' in result
+
+    def test_validate_valid_json(self):
+        assert validate_json('{"key": "value"}') is True
+
+    def test_validate_invalid_json(self):
+        with pytest.raises(Exception):
+            validate_json('not json')
+
+
+class TestJwtTool:
+    def test_decode_jwt(self):
+        token = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"
+        result = decode_jwt(token)
+        assert "header" in result
+        assert "payload" in result
+        assert result["payload"]["sub"] == "1234567890"
+
+    def test_decode_invalid_jwt(self):
+        with pytest.raises(ValueError):
+            decode_jwt("invalid.token")
+
+
+class TestCronTool:
+    def test_validate_simple_cron(self):
+        assert validate_cron("* * * * *") is True
+
+    def test_validate_specific_cron(self):
+        assert validate_cron("0 12 * * *") is True
+
+    def test_validate_invalid_cron(self):
+        assert validate_cron("invalid") is False
+
+    def test_get_next_run(self):
+        result = get_next_run("* * * * *")
+        assert result is not None
+
+
+class TestBase64Tool:
+    def test_encode_base64(self):
+        result = encode_base64("hello world")
+        assert result == "aGVsbG8gd29ybGQ="
+
+    def test_decode_base64(self):
+        result = decode_base64("aGVsbG8gd29ybGQ=")
+        assert result == "hello world"
+
+    def test_roundtrip(self):
+        original = "Test data with special chars: !@#$%"
+        encoded = encode_base64(original)
+        decoded = decode_base64(encoded)
+        assert original == decoded
+
+
+class TestUrlTool:
+    def test_encode_url(self):
+        result = encode_url("hello world")
+        assert result == "hello%20world"
+
+    def test_decode_url(self):
+        result = decode_url("hello%20world")
+        assert result == "hello world"
+
+    def test_roundtrip(self):
+        original = "https://example.com/path?query=value&other=123"
+        encoded = encode_url(original)
+        decoded = decode_url(encoded)
+        assert original == decoded