diff --git a/tests/test_parser.py b/tests/test_parser.py
new file mode 100644
index 0000000..5dafff1
--- /dev/null
+++ b/tests/test_parser.py
@@ -0,0 +1,313 @@
+"""Tests for the regex parser."""
+
+import pytest
+from regex_humanizer.parser import (
+    RegexParser,
+    parse_regex,
+    NodeType,
+    RegexNode,
+    LiteralNode,
+    CharacterClassNode,
+    QuantifierNode,
+    GroupNode,
+)
+
+
+class TestRegexParser:
+    """Test cases for RegexParser."""
+
+    def test_parse_simple_literal(self):
+        """Test parsing a simple literal string."""
+        parser = RegexParser("hello")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) == 1
+        assert ast.children[0].node_type == NodeType.LITERAL
+        assert ast.children[0].value == "hello"
+
+    def test_parse_digit_shorthand(self):
+        """Test parsing digit shorthand character class."""
+        parser = RegexParser("\\d+")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) == 1
+        quantifier = ast.children[0]
+        assert quantifier.node_type == NodeType.QUANTIFIER
+        assert quantifier.min_count == 1
+
+    def test_parse_character_class(self):
+        """Test parsing a character class."""
+        parser = RegexParser("[a-z]")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) == 1
+        child = ast.children[0]
+        assert child.node_type == NodeType.POSITIVE_SET
+        assert "a" in child.characters or len(child.ranges) > 0
+
+    def test_parse_negated_character_class(self):
+        """Test parsing a negated character class."""
+        parser = RegexParser("[^0-9]")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        child = ast.children[0]
+        assert child.node_type == NodeType.NEGATIVE_SET
+        assert child.negated is True
+
+    def test_parse_plus_quantifier(self):
+        """Test parsing a plus quantifier."""
+        parser = RegexParser("a+")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) == 1
+        quantifier = ast.children[0]
+        assert quantifier.node_type == NodeType.QUANTIFIER
+        assert quantifier.min_count == 1
+        assert quantifier.max_count == float('inf')
+
+    def test_parse_star_quantifier(self):
+        """Test parsing a star quantifier."""
+        parser = RegexParser("b*")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) == 1
+        quantifier = ast.children[0]
+        assert quantifier.node_type == NodeType.QUANTIFIER
+        assert quantifier.min_count == 0
+        assert quantifier.max_count == float('inf')
+
+    def test_parse_question_quantifier(self):
+        """Test parsing a question mark quantifier."""
+        parser = RegexParser("c?")
+        ast = parser.parse()
+
+        quantifier = ast.children[0]
+        assert quantifier.node_type == NodeType.QUANTIFIER
+        assert quantifier.min_count == 0
+        assert quantifier.max_count == 1
+
+    def test_parse_range_quantifier(self):
+        """Test parsing a range quantifier like {2,5}."""
+        parser = RegexParser("a{2,5}")
+        ast = parser.parse()
+
+        quantifier = ast.children[0]
+        assert quantifier.node_type == NodeType.QUANTIFIER
+        assert quantifier.min_count == 2
+        assert quantifier.max_count == 5
+
+    def test_parse_lazy_quantifier(self):
+        """Test parsing a lazy quantifier."""
+        parser = RegexParser("a+?")
+        ast = parser.parse()
+
+        quantifier = ast.children[0]
+        assert quantifier.node_type == NodeType.QUANTIFIER
+        assert quantifier.is_lazy is True
+
+    def test_parse_capturing_group(self):
+        """Test parsing a capturing group."""
+        parser = RegexParser("(hello)")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) == 1
+        group = ast.children[0]
+        assert group.node_type == NodeType.CAPTURING_GROUP
+        assert not group.is_non_capturing
+
+    def test_parse_non_capturing_group(self):
+        """Test parsing a non-capturing group."""
+        parser = RegexParser("(?:hello)")
+        ast = parser.parse()
+
+        group = ast.children[0]
+        assert group.node_type == NodeType.NON_CAPTURING_GROUP
+        assert group.is_non_capturing is True
+
+    def test_parse_named_group(self):
+        """Test parsing a named group."""
+        parser = RegexParser("(?P<name>hello)")
+        ast = parser.parse()
+
+        group = ast.children[0]
+        assert group.node_type == NodeType.NAMED_GROUP
+        assert group.name == "name"
+
+    def test_parse_positive_lookahead(self):
+        """Test parsing a positive lookahead."""
+        parser = RegexParser("(?=test)")
+        ast = parser.parse()
+
+        group = ast.children[0]
+        assert group.node_type == NodeType.LOOKAHEAD
+
+    def test_parse_negative_lookahead(self):
+        """Test parsing a negative lookahead."""
+        parser = RegexParser("(?!test)")
+        ast = parser.parse()
+
+        group = ast.children[0]
+        assert group.node_type == NodeType.NEGATIVE_LOOKAHEAD
+
+    def test_parse_lookbehind(self):
+        """Test parsing a lookbehind."""
+        parser = RegexParser("(?<=test)")
+        ast = parser.parse()
+
+        group = ast.children[0]
+        assert group.node_type == NodeType.LOOKBEHIND
+
+    def test_parse_anchor_start(self):
+        """Test parsing a start anchor."""
+        parser = RegexParser("^start")
+        ast = parser.parse()
+
+        assert ast.children[0].node_type == NodeType.ANCHOR_START
+
+    def test_parse_anchor_end(self):
+        """Test parsing an end anchor."""
+        parser = RegexParser("end$")
+        ast = parser.parse()
+
+        anchor = ast.children[-1]
+        assert anchor.node_type == NodeType.ANCHOR_END
+
+    def test_parse_word_boundary(self):
+        """Test parsing a word boundary."""
+        parser = RegexParser("\\bword\\b")
+        ast = parser.parse()
+
+        assert any(child.node_type == NodeType.WORD_BOUNDARY for child in ast.children)
+
+    def test_parse_dot(self):
+        """Test parsing a dot (any character)."""
+        parser = RegexParser(".")
+        ast = parser.parse()
+
+        assert ast.children[0].node_type == NodeType.DOT
+
+    def test_parse_complex_pattern(self):
+        """Test parsing a complex regex pattern."""
+        pattern = r"^(?:http|https)://[\w.-]+\.(?:com|org|net)$"
+        parser = RegexParser(pattern)
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) > 0
+
+    def test_parse_alternation(self):
+        """Test parsing alternation with pipe."""
+        parser = RegexParser("cat|dog")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) >= 1
+
+    def test_parse_escaped_character(self):
+        """Test parsing escaped characters."""
+        parser = RegexParser("\\.")
+        ast = parser.parse()
+
+        assert len(ast.children) > 0
+
+    def test_parse_whitespace_shorthand(self):
+        """Test parsing whitespace shorthand."""
+        parser = RegexParser("\\s+")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        quantifier = ast.children[0]
+        assert quantifier.node_type == NodeType.QUANTIFIER
+
+    def test_parse_word_char_shorthand(self):
+        """Test parsing word character shorthand."""
+        parser = RegexParser("\\w*")
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+
+    def test_parse_hex_escape(self):
+        """Test parsing hex escape sequence."""
+        parser = RegexParser("\\x41")
+        ast = parser.parse()
+
+        assert len(ast.children) > 0
+
+    def test_parse_backreference(self):
+        """Test parsing a backreference."""
+        parser = RegexParser("(a)\\1")
+        ast = parser.parse()
+
+        assert len(ast.children) > 0
+
+    def test_parse_empty_group(self):
+        """Test parsing an empty group."""
+        parser = RegexParser("()")
+        ast = parser.parse()
+
+        group = ast.children[0]
+        assert group.node_type == NodeType.CAPTURING_GROUP
+
+    def test_parse_nested_groups(self):
+        """Test parsing nested groups."""
+        parser = RegexParser("((a)(b))")
+        ast = parser.parse()
+
+        assert len(ast.children) == 1
+
+    def test_errors_empty(self):
+        """Test that valid patterns have no errors."""
+        parser = RegexParser("hello")
+        parser.parse()
+
+        assert len(parser.get_errors()) == 0
+
+    def test_parse_email_pattern(self):
+        """Test parsing a typical email regex pattern."""
+        pattern = r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}"
+        parser = RegexParser(pattern)
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+        assert len(ast.children) > 0
+
+    def test_parse_phone_pattern(self):
+        """Test parsing a phone number regex."""
+        pattern = r"\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}"
+        parser = RegexParser(pattern)
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+
+    def test_parse_date_pattern(self):
+        """Test parsing a date regex."""
+        pattern = r"\d{4}-\d{2}-\d{2}"
+        parser = RegexParser(pattern)
+        ast = parser.parse()
+
+        assert ast.node_type == NodeType.SEQUENCE
+
+
+class TestNodeTypes:
+    """Test node type enumeration."""
+
+    def test_node_type_values(self):
+        """Test that all expected node types exist."""
+        expected_types = [
+            "LITERAL", "CHARACTER_CLASS", "POSITIVE_SET", "NEGATIVE_SET",
+            "DOT", "GROUP", "CAPTURING_GROUP", "NON_CAPTURING_GROUP",
+            "NAMED_GROUP", "LOOKAHEAD", "LOOKBEHIND", "NEGATIVE_LOOKAHEAD",
+            "NEGATIVE_LOOKBEHIND", "QUANTIFIER", "ANCHOR_START", "ANCHOR_END",
+            "WORD_BOUNDARY", "START_OF_STRING", "END_OF_STRING", "DIGIT",
+            "NON_DIGIT", "WORD_CHAR", "WHITESPACE", "BACKREFERENCE",
+        ]
+
+        for type_name in expected_types:
+            assert hasattr(NodeType, type_name), f"Missing node type: {type_name}"