diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..37ff412
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,251 @@
+"""Tests for CLI commands."""
+
+import pytest
+import tempfile
+import os
+from click.testing import CliRunner
+from pathlib import Path
+
+
+class TestCLIConvert:
+    """Tests for convert command."""
+    
+    def test_convert_json_to_yaml(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.json', delete=False) as f:
+            f.write('{"name": "test", "value": 123}')
+            temp_input = f.name
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.yaml', delete=False) as f:
+            temp_output = f.name
+        
+        try:
+            result = runner.invoke(cli, ['convert', temp_input, '--to', 'yaml', '-o', temp_output])
+            assert result.exit_code == 0
+            assert Path(temp_output).read_text().strip() != ""
+        finally:
+            os.unlink(temp_input)
+            if os.path.exists(temp_output):
+                os.unlink(temp_output)
+    
+    def test_convert_yaml_to_json(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.yaml', delete=False) as f:
+            f.write('name: test\nvalue: 123')
+            temp_input = f.name
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.json', delete=False) as f:
+            temp_output = f.name
+        
+        try:
+            result = runner.invoke(cli, ['convert', temp_input, '--to', 'json', '-o', temp_output])
+            assert result.exit_code == 0
+            assert Path(temp_output).read_text().strip() != ""
+        finally:
+            os.unlink(temp_input)
+            if os.path.exists(temp_output):
+                os.unlink(temp_output)
+    
+    def test_convert_with_indent(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.json', delete=False) as f:
+            f.write('{"name": "test"}')
+            temp_input = f.name
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.yaml', delete=False) as f:
+            temp_output = f.name
+        
+        try:
+            result = runner.invoke(cli, ['convert', temp_input, '--to', 'yaml', '-o', temp_output, '--indent', '4'])
+            assert result.exit_code == 0
+        finally:
+            os.unlink(temp_input)
+            if os.path.exists(temp_output):
+                os.unlink(temp_output)
+    
+    def test_convert_invalid_format(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['convert', '--to', 'invalid'])
+        assert result.exit_code != 0
+    
+    def test_convert_stdin_to_stdout(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['convert', '-f', 'json', '--to', 'yaml'], input='{"test": 123}')
+        assert result.exit_code == 0
+
+
+class TestCLIValidate:
+    """Tests for validate command."""
+    
+    def test_validate_valid_json(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.json', delete=False) as f:
+            f.write('{"name": "test"}')
+            temp_file = f.name
+        
+        try:
+            result = runner.invoke(cli, ['validate', temp_file])
+            assert result.exit_code == 0
+        finally:
+            os.unlink(temp_file)
+    
+    def test_validate_invalid_json(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.json', delete=False) as f:
+            f.write('{invalid json}')
+            temp_file = f.name
+        
+        try:
+            result = runner.invoke(cli, ['validate', temp_file])
+            assert result.exit_code != 0
+        finally:
+            os.unlink(temp_file)
+    
+    def test_validate_yaml_file(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.yaml', delete=False) as f:
+            f.write('name: test')
+            temp_file = f.name
+        
+        try:
+            result = runner.invoke(cli, ['validate', temp_file])
+            assert result.exit_code == 0
+        finally:
+            os.unlink(temp_file)
+    
+    def test_validate_with_format_option(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        with tempfile.NamedTemporaryFile(mode='w', suffix='.txt', delete=False) as f:
+            f.write('{"name": "test"}')
+            temp_file = f.name
+        
+        try:
+            result = runner.invoke(cli, ['validate', temp_file, '--format', 'json'])
+            assert result.exit_code == 0
+        finally:
+            os.unlink(temp_file)
+    
+    def test_validate_stdin(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['validate', '--stdin', '--format', 'json'], input='{"test": 1}')
+        assert result.exit_code == 0
+
+
+class TestCLIInfo:
+    """Tests for info command."""
+    
+    def test_info_command(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['info'])
+        assert result.exit_code == 0
+        assert "Supported Formats" in result.output
+
+
+class TestCLIHelp:
+    """Tests for CLI help."""
+    
+    def test_main_help(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['--help'])
+        assert result.exit_code == 0
+        assert "Data Format Converter" in result.output
+    
+    def test_convert_help(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['convert', '--help'])
+        assert result.exit_code == 0
+        assert "Convert data from one format to another" in result.output
+    
+    def test_validate_help(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['validate', '--help'])
+        assert result.exit_code == 0
+        assert "Validate syntax" in result.output
+    
+    def test_tui_help(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['tui', '--help'])
+        assert result.exit_code == 0
+        assert "interactive TUI mode" in result.output
+    
+    def test_watch_help(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['watch', '--help'])
+        assert result.exit_code == 0
+        assert "Watch files for changes" in result.output
+
+
+class TestCLIEdgeCases:
+    """Tests for edge cases and error handling."""
+    
+    def test_convert_missing_file(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['convert', 'nonexistent.json', '--to', 'yaml'])
+        assert result.exit_code != 0
+    
+    def test_convert_invalid_source_format(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['convert', '--from', 'invalid', '--to', 'yaml'])
+        assert result.exit_code != 0
+    
+    def test_validate_missing_file(self):
+        from src.cli import cli
+        
+        runner = CliRunner()
+        
+        result = runner.invoke(cli, ['validate', 'nonexistent.json'])
+        assert result.exit_code != 0