diff --git a/easygraph/functions/drawing/geometry.py b/easygraph/functions/drawing/geometry.py
index b3e9981d..4e71dc63 100644
--- a/easygraph/functions/drawing/geometry.py
+++ b/easygraph/functions/drawing/geometry.py
@@ -25,6 +25,8 @@ def vlen(vector):
 
 def common_tangent_radian(r1, r2, d):
     value = abs(r2 - r1) / d
+    if value > 1.0: value = 1.0
+    elif value < -1.0: value = -1.0
     alpha = math.acos(value)
     alpha = alpha if r1 > r2 else pi - alpha
     return alpha
diff --git a/easygraph/tests/test_hif.py b/easygraph/tests/test_hif.py
new file mode 100644
index 00000000..a598bdc6
--- /dev/null
+++ b/easygraph/tests/test_hif.py
@@ -0,0 +1,95 @@
+import unittest
+import json
+import os
+import tempfile
+import easygraph as eg
+from pathlib import Path
+
+MOCK_HIF_DATA = {
+    "metadata": {
+        "name": "test_organism",
+        "description": "Simulation for unit test"
+    },
+    "network-type": "directed",
+    "nodes": [
+        {"node": "n1", "weight": 1.0, "attrs": {"name": "Node A"}},
+        {"node": "n2", "weight": 1.0, "attrs": {"name": "Node B"}}
+    ],
+    "edges": [
+        {"edge": "e1", "weight": 1.0, "attrs": {"name": "Edge Alpha"}}
+    ],
+    "incidences": [
+        {"edge": "e1", "node": "n1", "weight": 1.0, "direction": "tail"},
+        {"edge": "e1", "node": "n2", "weight": 1.0, "direction": "head"}
+    ]
+}
+
+class HIFTest(unittest.TestCase):
+    def setUp(self):
+        self.temp_dir = tempfile.TemporaryDirectory()
+        self.temp_dir_path = Path(self.temp_dir.name)
+        
+        self.input_file = self.temp_dir_path / "input_mock.hif.json"
+        self.output_file = self.temp_dir_path / "output_result.hif.json"
+
+        with open(self.input_file, "w", encoding="utf-8") as f:
+            json.dump(MOCK_HIF_DATA, f)
+
+    def tearDown(self):
+        self.temp_dir.cleanup()
+
+    def test_hif_roundtrip_preservation(self):
+        """
+        Test that custom attributes are preserved AND the generated
+        EasyGraph object is structurally valid.
+        """
+        hg = eg.hif_to_hypergraph(filename=self.input_file)
+       
+        self.assertEqual(hg.num_v, 2, "Loaded graph should have 2 nodes")
+        self.assertEqual(hg.num_e, 1, "Loaded graph should have 1 edge")
+        
+        node_names = [props.get('name') for props in hg.v_property]
+        self.assertIn("n1", node_names, "Node ID 'n1' should be in v_property")
+        
+        edges = hg.e[0]
+        self.assertEqual(len(edges), 1, "Should have 1 edge group")
+        self.assertEqual(len(edges[0]), 2, "Edge e1 should connect 2 nodes")
+        
+        self.assertTrue(hasattr(hg, "custom_hif_incidences"), "Failed to attach custom incidences")
+        self.assertTrue(hasattr(hg, "metadata"), "Failed to attach metadata")
+
+        eg.hypergraph_to_hif(hg, filename=self.output_file)
+        
+        with open(self.output_file, 'r', encoding="utf-8") as f:
+            res = json.load(f)
+            
+            first_incidence = res["incidences"][0]
+            self.assertIn("direction", first_incidence, "'direction' field lost in roundtrip")
+            self.assertIn(first_incidence["direction"], ["tail", "head"])
+            
+            self.assertNotIn("default_attrs", res["metadata"], "'default_attrs' was forced into metadata")
+            self.assertEqual(res["metadata"]["name"], "test_organism")
+
+    def test_manual_graph_export(self):
+        """Test exporting a manually created Hypergraph (not loaded from file)."""
+        hg = eg.Hypergraph(
+            num_v=5, 
+            e_list=[(0, 1, 2), (2, 3), (2, 3), (0, 4)], 
+            merge_op="sum"
+        )
+        hg.metadata = {"created_by": "manual_test"}
+
+        eg.hypergraph_to_hif(hg, filename=self.output_file)
+        
+        with open(self.output_file, 'r', encoding="utf-8") as f:
+            data = json.load(f)
+            self.assertEqual(len(data["nodes"]), 5)
+            self.assertEqual(len(data["edges"]), 3) 
+            self.assertEqual(data["metadata"]["created_by"], "manual_test")
+            
+
+            weights = [e["weight"] for e in data["edges"]]
+            self.assertIn(2.0, weights, "Merged edge weight should be 2.0")
+
+if __name__ == "__main__":
+    unittest.main()
\ No newline at end of file
diff --git a/easygraph/utils/HIF.py b/easygraph/utils/HIF.py
new file mode 100644
index 00000000..ea536163
--- /dev/null
+++ b/easygraph/utils/HIF.py
@@ -0,0 +1,233 @@
+import json
+import requests
+import fastjsonschema
+from copy import deepcopy
+from typing import Optional, Union, List, Dict, Any
+from pathlib import Path
+from easygraph.classes.hypergraph import Hypergraph
+
+schema_url = "https://raw.githubusercontent.com/pszufe/HIF_validators/main/schemas/hif_schema_v0.1.0.json"
+
+class EasyGraphHIFError(Exception):
+    """Custom exception for HIF conversion errors."""
+    pass
+
+_hif_validator = None
+
+def _get_hif_validator():
+    global _hif_validator
+    if _hif_validator is None:
+        try:
+            resp = requests.get(schema_url, timeout=5)
+            if resp.status_code == 200:
+                schema = json.loads(resp.text)
+                _hif_validator = fastjsonschema.compile(schema)
+        except Exception:
+            print("Warning: HIF Schema could not be fetched. Validation skipped.")
+            _hif_validator = lambda x: True
+            
+    return _hif_validator if _hif_validator else (lambda x: True)
+
+def hypergraph_to_hif(
+    hg: Hypergraph,
+    filename: Optional[Union[str, Path]] = None,
+) -> dict:
+    """
+    Converts an EasyGraph Hypergraph to HIF JSON.
+    Correctly handles hg.e tuple structure ((edges), (weights), (props)).
+    """
+    
+    if hasattr(hg, "custom_hif_nodes"):
+        nodj = hg.custom_hif_nodes
+    else:
+        nodj = []
+        num_v = hg.num_v if hasattr(hg, "num_v") else len(hg.v_property) if hasattr(hg, "v_property") else 0
+        v_props = getattr(hg, "v_property", [{} for _ in range(num_v)])
+        if not v_props and num_v > 0: v_props = [{} for _ in range(num_v)]
+
+        for i in range(num_v):
+            props = v_props[i] if i < len(v_props) and isinstance(v_props[i], dict) else {}
+            p = props.copy()
+            weight = p.pop("weight", 1.0)
+            node_id = p.pop("name", str(i))
+            nodj.append({"node": node_id, "weight": weight, "attrs": p})
+
+    e_structure = []
+    e_weights = []
+    e_props = []
+
+    if hasattr(hg, "e") and isinstance(hg.e, tuple) and len(hg.e) == 3 and \
+       isinstance(hg.e[0], (list, tuple)) and isinstance(hg.e[1], (list, tuple)):
+        e_structure = hg.e[0]
+        e_weights = hg.e[1]
+        e_props = hg.e[2]
+        
+    elif hasattr(hg, "e_list") and hg.e_list:
+        e_structure = hg.e_list
+        e_weights = getattr(hg, "e_weight", [1.0] * len(e_structure))
+        e_props = getattr(hg, "e_property_full", [{} for _ in range(len(e_structure))])
+        
+    elif hasattr(hg, "e") and isinstance(hg.e, (list, tuple)):
+        e_structure = hg.e
+        e_weights = getattr(hg, "e_weight", [1.0] * len(e_structure))
+        e_props = getattr(hg, "e_property_full", [{} for _ in range(len(e_structure))])
+
+    num_e = len(e_structure)
+    
+    if len(e_weights) < num_e: e_weights = [1.0] * num_e
+    if len(e_props) < num_e: e_props = [{} for _ in range(num_e)]
+
+    if hasattr(hg, "custom_hif_edges"):
+        edgj = hg.custom_hif_edges
+    else:
+        edgj = []
+        for i in range(num_e):
+            props = e_props[i].copy() if isinstance(e_props[i], dict) else {}
+            edge_id = props.pop("name", str(i))
+            weight = e_weights[i]
+            props.pop("weight", None)
+            edgj.append({"edge": edge_id, "weight": weight, "attrs": props})
+
+    if hasattr(hg, "custom_hif_incidences"):
+        incj = hg.custom_hif_incidences
+    else:
+        incj = []
+        node_id_list = [n["node"] for n in nodj]
+        edge_id_list = [e["edge"] for e in edgj]
+        
+        for e_idx, nodes_in_edge in enumerate(e_structure):
+            if e_idx >= len(edge_id_list): break
+            edge_name = edge_id_list[e_idx]
+            
+            flat_nodes = []
+            if isinstance(nodes_in_edge, (list, tuple)):
+                for item in nodes_in_edge:
+                    if isinstance(item, (list, tuple)):
+                        flat_nodes.extend(item)
+                    else:
+                        flat_nodes.append(item)
+            else:
+                flat_nodes = [nodes_in_edge]
+
+            for n_idx in flat_nodes:
+                try:
+                    n_idx_int = int(n_idx)
+                    if 0 <= n_idx_int < len(node_id_list):
+                        incj.append({
+                            "edge": edge_name,
+                            "node": node_id_list[n_idx_int],
+                            "weight": 1.0, 
+                        })
+                except (ValueError, TypeError):
+                    continue
+
+    metadata = getattr(hg, "metadata", {})
+    network_type = getattr(hg, "network_type", "undirected")
+
+    hif = {
+        "nodes": nodj,
+        "edges": edgj,
+        "incidences": incj,
+        "network-type": network_type,
+        "metadata": metadata
+    }
+
+    try:
+        validator = _get_hif_validator()
+        validator(hif)
+    except Exception as e:
+        print(f"Validation Warning: {e}") 
+
+    if filename:
+        with open(filename, "w", encoding='utf-8') as f:
+            json.dump(hif, f, indent=4, ensure_ascii=False)
+            
+    return hif
+
+
+def hif_to_hypergraph(
+    hif: dict = None,
+    filename: Optional[Union[str, Path]] = None,
+):
+    """
+    Reads HIF JSON and returns an EasyGraph Hypergraph.
+    Attaches original JSON parts to 'custom_hif_*' attributes to preserve
+    structure during round-trips.
+    """
+    if hif is None:
+        if filename is None:
+            raise EasyGraphHIFError("No HIF data or filename provided.")
+        try:
+            with open(filename, "r", encoding='utf-8') as f:
+                hif = json.load(f)
+        except Exception as e:
+            raise EasyGraphHIFError(f"Failed to load HIF file {filename}: {e}")
+
+    nodes_list = hif.get("nodes", [])
+    node_name_to_idx = {rec["node"]: i for i, rec in enumerate(nodes_list)}
+    num_v = len(nodes_list)
+
+    edges_list = hif.get("edges", [])
+    edge_name_to_idx = {rec["edge"]: i for i, rec in enumerate(edges_list)}
+    num_e = len(edges_list)
+
+    v_property = [{} for _ in range(num_v)]
+    for rec in nodes_list:
+        idx = node_name_to_idx.get(rec["node"])
+        if idx is not None:
+
+            prop = rec.get("attrs", {}).copy()
+            prop["name"] = rec["node"] 
+            prop["weight"] = rec.get("weight", 1.0)
+            v_property[idx] = prop
+
+    e_property_full = [{} for _ in range(num_e)]
+    e_weight = [1.0] * num_e
+    
+    for rec in edges_list:
+        idx = edge_name_to_idx.get(rec["edge"])
+        if idx is not None:
+            prop = rec.get("attrs", {}).copy()
+            if "name" not in prop:
+                prop["name"] = rec["edge"]
+            
+            prop["weight"] = rec.get("weight", 1.0)
+            e_property_full[idx] = prop
+            e_weight[idx] = prop["weight"]
+
+    raw_groups = [[] for _ in range(num_e)]
+    
+    incidences_list = hif.get("incidences", [])
+    
+    for inc in incidences_list:
+        e_name = inc.get("edge")
+        n_name = inc.get("node")
+        
+        e_idx = edge_name_to_idx.get(e_name)
+        n_idx = node_name_to_idx.get(n_name)
+        
+        if e_idx is not None and n_idx is not None:
+            raw_groups[e_idx].append(n_idx)
+
+    hg = Hypergraph(
+        num_v=num_v,
+        e_list=raw_groups,
+        e_weight=e_weight,
+        v_property=v_property
+    )
+    
+    hg.custom_hif_nodes = deepcopy(nodes_list)
+    hg.custom_hif_edges = deepcopy(edges_list)
+    hg.custom_hif_incidences = deepcopy(incidences_list)
+    
+    if "metadata" in hif:
+        hg.metadata = deepcopy(hif["metadata"])
+    else:
+        hg.metadata = {}
+        
+    if "network-type" in hif:
+        hg.network_type = hif["network-type"]
+        
+    hg.e_property_full = e_property_full
+
+    return hg
\ No newline at end of file
diff --git a/easygraph/utils/__init__.py b/easygraph/utils/__init__.py
index 1005a65d..7629c893 100644
--- a/easygraph/utils/__init__.py
+++ b/easygraph/utils/__init__.py
@@ -11,3 +11,4 @@
 from easygraph.utils.relabel import *
 from easygraph.utils.sparse import *
 from easygraph.utils.type_change import *
+from easygraph.utils.HIF import *
\ No newline at end of file