diff --git a/src/docgen/generators/openapi.py b/src/docgen/generators/openapi.py
new file mode 100644
index 0000000..7182e11
--- /dev/null
+++ b/src/docgen/generators/openapi.py
@@ -0,0 +1,95 @@
+"""OpenAPI documentation generator."""
+
+import json
+from pathlib import Path
+from typing import Any
+from docgen.models import DocConfig, Endpoint, HTTPMethod
+from docgen.generators import BaseGenerator
+
+
+class OpenAPIGenerator(BaseGenerator):
+    """Generator for OpenAPI 3.0 specification."""
+
+    def generate(self, endpoints: list[Endpoint], output_dir: Path) -> Path:
+        """Generate OpenAPI specification."""
+        output_dir = self._ensure_output_dir(output_dir)
+
+        spec = self._build_openapi_spec(endpoints)
+        spec_path = output_dir / "openapi.json"
+        spec_path.write_text(json.dumps(spec, indent=2))
+
+        return spec_path
+
+    def _build_openapi_spec(self, endpoints: list[Endpoint]) -> dict[str, Any]:
+        """Build the OpenAPI specification dictionary."""
+        spec = {
+            "openapi": "3.0.3",
+            "info": {
+                "title": self.config.title,
+                "description": self.config.description,
+                "version": self.config.version,
+            },
+            "paths": {},
+            "servers": [{"url": "/"}],
+        }
+
+        for endpoint in endpoints:
+            path_item = self._endpoint_to_path_item(endpoint)
+            
+            if endpoint.path not in spec["paths"]:
+                spec["paths"][endpoint.path] = path_item
+            else:
+                existing = spec["paths"][endpoint.path]
+                for method in ["get", "post", "put", "patch", "delete", "options", "head"]:
+                    if method in path_item:
+                        existing[method] = path_item[method]
+
+        return spec
+
+    def _endpoint_to_path_item(self, endpoint: Endpoint) -> dict[str, Any]:
+        """Convert an Endpoint to OpenAPI path item."""
+        method = endpoint.method.value.lower()
+        
+        operation = {
+            "summary": endpoint.summary or f"{endpoint.method.value} {endpoint.path}",
+            "description": endpoint.description,
+            "operationId": endpoint.operation_id or f"{method}_{endpoint.path.replace('/', '_').strip('_')}",
+            "deprecated": endpoint.deprecated,
+            "parameters": [self._param_to_openapi(p) for p in endpoint.parameters],
+            "responses": self._build_responses(endpoint.responses),
+        }
+
+        if endpoint.security:
+            operation["security"] = [{"bearerAuth": []}]
+
+        return {method: operation}
+
+    def _param_to_openapi(self, param) -> dict[str, Any]:
+        """Convert Parameter to OpenAPI parameter."""
+        return {
+            "name": param.name,
+            "in": param.location.value,
+            "description": param.description,
+            "required": param.required,
+            "schema": {"type": param.type, "default": param.default},
+            "example": param.example,
+        }
+
+    def _build_responses(self, responses) -> dict[str, Any]:
+        """Build OpenAPI responses object."""
+        if not responses:
+            return {
+                "200": {"description": "Successful response"},
+                "default": {"description": "Error response"},
+            }
+        
+        result = {}
+        for resp in responses:
+            resp_obj = {"description": resp.description}
+            if resp.example:
+                resp_obj["content"] = {
+                    resp.content_type: {"schema": resp.example}
+                }
+            result[str(resp.status_code)] = resp_obj
+        
+        return result