diff --git a/vibeguard/patterns/definitions.py b/vibeguard/patterns/definitions.py
new file mode 100644
index 0000000..4d7fc9f
--- /dev/null
+++ b/vibeguard/patterns/definitions.py
@@ -0,0 +1,64 @@
+"""Pattern definitions for VibeGuard."""
+
+from dataclasses import dataclass, field
+from enum import Enum
+from typing import Any
+
+
+class Severity(Enum):
+    """Severity levels for detected issues."""
+
+    CRITICAL = "critical"
+    ERROR = "error"
+    WARNING = "warning"
+    INFO = "info"
+
+
+@dataclass
+class Pattern:
+    """Definition of an anti-pattern."""
+
+    id: str
+    name: str
+    description: str
+    severity: Severity
+    languages: list[str]
+    message: str
+    suggestion: str
+    query: str = ""
+    before_example: str = ""
+    after_example: str = ""
+    category: str = "general"
+
+
+@dataclass
+class Issue:
+    """A detected issue in the code."""
+
+    pattern_id: str
+    file: str
+    line: int
+    severity: Severity
+    message: str
+    suggestion: str
+    language: str = ""
+    column: int = 0
+    end_line: int = 0
+    end_column: int = 0
+    code_snippet: str = ""
+
+    def to_dict(self) -> dict[str, Any]:
+        """Convert issue to dictionary."""
+        return {
+            "pattern": self.pattern_id,
+            "file": self.file,
+            "line": self.line,
+            "severity": self.severity.value,
+            "message": self.message,
+            "suggestion": self.suggestion,
+            "language": self.language,
+            "column": self.column,
+            "end_line": self.end_line,
+            "end_column": self.end_column,
+            "code_snippet": self.code_snippet,
+        }