diff --git a/dfgraph/__init__.py b/dfgraph/__init__.py
new file mode 100644
index 0000000..8c2ec92
--- /dev/null
+++ b/dfgraph/__init__.py
@@ -0,0 +1 @@
+"""Dataflow graph renderer for OR1 dfasm programs."""
diff --git a/dfgraph/__main__.py b/dfgraph/__main__.py
new file mode 100644
index 0000000..6f98f11
--- /dev/null
+++ b/dfgraph/__main__.py
@@ -0,0 +1,39 @@
+"""CLI entry point: python -m dfgraph path/to/file.dfasm [--port 8420]"""
+
+import argparse
+import sys
+from pathlib import Path
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(
+        prog="dfgraph",
+        description="Visualise a dfasm dataflow program as an interactive graph.",
+    )
+    parser.add_argument(
+        "file",
+        type=Path,
+        help="Path to the .dfasm source file to visualise",
+    )
+    parser.add_argument(
+        "--port",
+        type=int,
+        default=8420,
+        help="Port for the web server (default: 8420)",
+    )
+
+    args = parser.parse_args()
+
+    if not args.file.exists():
+        print(f"Error: file not found: {args.file}", file=sys.stderr)
+        sys.exit(1)
+
+    if not args.file.suffix == ".dfasm":
+        print(f"Warning: expected .dfasm file, got: {args.file.suffix}", file=sys.stderr)
+
+    # Server startup will be added in Phase 4
+    print(f"dfgraph: would serve {args.file} on port {args.port}")
+
+
+if __name__ == "__main__":
+    main()