diff --git a/core/builder/tests/test_bundle_reader.py b/core/builder/tests/test_bundle_reader.py
new file mode 100644
index 0000000000..1a51e318dd
--- /dev/null
+++ b/core/builder/tests/test_bundle_reader.py
@@ -0,0 +1,198 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+import json
+import struct
+from pathlib import Path
+from typing import Any
+
+import pytest
+
+from tensorrt_model_connect.bundle_writer import BUNDLE_MAGIC, _MAX_HEADER_SIZE
+
+
+def _detect_duplicate_keys(pairs: list[tuple[str, Any]]) -> dict[str, Any]:
+    seen: dict[str, Any] = {}
+    for key, value in pairs:
+        if key in seen:
+            raise ValueError(f"Duplicate section name: {key!r}")
+        seen[key] = value
+    return seen
+
+
+class BundleReader:
+    """Read named sections from a bundle produced by BundleWriter."""
+
+    def __init__(self, path: str | Path) -> None:
+        self._path = Path(path)
+        with self._path.open("rb") as f:
+            magic = f.read(len(BUNDLE_MAGIC))
+            if magic != BUNDLE_MAGIC:
+                raise ValueError(
+                    f"Invalid bundle magic signature: expected {BUNDLE_MAGIC!r}, got {magic!r}"
+                )
+            (header_size,) = struct.unpack("<Q", f.read(8))
+            if header_size > _MAX_HEADER_SIZE:
+                raise ValueError("bundle header exceeds the 100 MiB runtime limit")
+            header_bytes = f.read(header_size)
+            self._data_start = len(BUNDLE_MAGIC) + 8 + header_size
+            file_size = self._path.stat().st_size
+            self._data_size = file_size - self._data_start
+
+        try:
+            header: dict[str, Any] = json.loads(
+                header_bytes, object_pairs_hook=_detect_duplicate_keys
+            )
+        except json.JSONDecodeError as exc:
+            raise ValueError(f"bundle header is not valid JSON: {exc}") from exc
+
+        if "sections" not in header:
+            raise ValueError("bundle header missing 'sections' key")
+        raw_sections = header["sections"]
+        if not isinstance(raw_sections, dict):
+            raise ValueError("bundle header 'sections' must be a JSON object")
+
+        sections: dict[str, tuple[int, int]] = {}
+        for name, entry in raw_sections.items():
+            offset = entry.get("offset")
+            length = entry.get("length")
+            if not isinstance(offset, int) or not isinstance(length, int):
+                raise ValueError(
+                    f"section {name!r}: offset and length must be integers"
+                )
+            if offset < 0 or length < 0:
+                raise ValueError(
+                    f"section {name!r}: offset and length must be non-negative"
+                )
+            if offset + length > self._data_size:
+                raise ValueError(
+                    f"section {name!r}: goes out-of-file range "
+                    f"(offset={offset}, length={length}, data_size={self._data_size})"
+                )
+            sections[name] = (offset, length)
+
+        # Overlap check: sort by offset and verify no two sections overlap.
+        sorted_sections = sorted(sections.items(), key=lambda kv: kv[1][0])
+        for i in range(len(sorted_sections) - 1):
+            name_a, (off_a, len_a) = sorted_sections[i]
+            name_b, (off_b, _) = sorted_sections[i + 1]
+            if off_a + len_a > off_b:
+                raise ValueError(
+                    f"Sections overlap: {name_a!r} ends at {off_a + len_a}, "
+                    f"but {name_b!r} starts at {off_b}"
+                )
+
+        self._sections = sections
+
+    def read_section(self, name: str) -> bytes:
+        """Read and return the raw bytes of a named section."""
+
+        if name not in self._sections:
+            raise KeyError(f"bundle has no section named {name!r}")
+        offset, length = self._sections[name]
+        with self._path.open("rb") as f:
+            f.seek(self._data_start + offset)
+            return f.read(length)
+
+
+
+def create_bundle(path, magic, header, sections_data):
+    header_str = json.dumps(header).encode("utf-8")
+    with open(path, "wb") as f:
+        f.write(magic)
+        f.write(struct.pack("<Q", len(header_str)))
+        f.write(header_str)
+        for data in sections_data:
+            f.write(data)
+
+def test_valid_bundle(tmp_path):
+    p = tmp_path / "valid.bundle"
+    header = {
+        "model_id": "test",
+        "sections": {
+            "config": {"offset": 0, "length": 4},
+            "weights": {"offset": 4, "length": 8},
+        },
+    }
+    create_bundle(p, BUNDLE_MAGIC, header, [b"conf", b"weightss"])
+    reader = BundleReader(p)
+    assert reader.read_section("config") == b"conf"
+    assert reader.read_section("weights") == b"weightss"
+
+def test_invalid_magic(tmp_path):
+    p = tmp_path / "invalid_magic.bundle"
+    header = {"sections": {}}
+    create_bundle(p, b"BADMAGIC", header, [])
+    with pytest.raises(ValueError, match="Invalid bundle magic signature"):
+        BundleReader(p)
+
+
+def test_missing_sections(tmp_path):
+    p = tmp_path / "missing_sections.bundle"
+    header = {"model_id": "test"}
+    create_bundle(p, BUNDLE_MAGIC, header, [])
+    with pytest.raises(ValueError, match="missing 'sections' key"):
+        BundleReader(p)
+
+def test_invalid_offset_type(tmp_path):
+    p = tmp_path / "invalid_offset.bundle"
+    header = {
+        "sections": {
+            "config": {"offset": "0", "length": 4},
+        },
+    }
+    create_bundle(p, BUNDLE_MAGIC, header, [b"conf"])
+    with pytest.raises(ValueError, match="offset and length must be integers"):
+        BundleReader(p)
+
+
+def test_negative_offset(tmp_path):
+    p = tmp_path / "negative_offset.bundle"
+    header = {
+        "sections": {
+            "config": {"offset": -1, "length": 4},
+        },
+    }
+    create_bundle(p, BUNDLE_MAGIC, header, [b"conf"])
+    with pytest.raises(ValueError, match="offset and length must be non-negative"):
+        BundleReader(p)
+
+
+def test_overlapping_sections(tmp_path):
+    p = tmp_path / "overlap.bundle"
+    header = {
+        "sections": {
+            "config": {"offset": 0, "length": 4},
+            "weights": {"offset": 2, "length": 4},
+        },
+    }
+    create_bundle(p, BUNDLE_MAGIC, header, [b"overlap_"])
+    with pytest.raises(ValueError, match="Sections overlap"):
+        BundleReader(p)
+
+
+def test_out_of_file_range(tmp_path):
+    p = tmp_path / "out_of_range.bundle"
+    header = {
+        "sections": {
+            "config": {"offset": 0, "length": 100},
+        },
+    }
+    create_bundle(p, BUNDLE_MAGIC, header, [b"short"])
+    with pytest.raises(ValueError, match="goes out-of-file range"):
+        BundleReader(p)
+
+
+def test_duplicate_sections(tmp_path):
+    """Bundles with duplicate section names in JSON must be rejected."""
+    p = tmp_path / "duplicate.bundle"
+    # Craft raw bytes: json.dumps deduplicates keys, so write raw bytes.
+    raw_sections = b'"config":{"offset":0,"length":4},"config":{"offset":4,"length":4}'
+    header_str = b'{"sections":{' + raw_sections + b"}}"  # deliberately invalid JSON key duplication
+    with open(p, "wb") as f:
+        f.write(BUNDLE_MAGIC)
+        f.write(struct.pack("<Q", len(header_str)))
+        f.write(header_str)
+        f.write(b"confconf")
+    with pytest.raises(ValueError, match="Duplicate section name"):
+        BundleReader(p)
diff --git a/tools/tests/test_architecture.py b/tools/tests/test_architecture.py
index f7a594ad63..e7e80985c0 100644
--- a/tools/tests/test_architecture.py
+++ b/tools/tests/test_architecture.py
@@ -271,6 +271,7 @@ def test_shared_python_and_native_trees_are_closed_minimal_sets() -> None:
         "core/builder/tests/__init__.py",
         "core/builder/tests/test_build.py",
         "core/builder/tests/test_build_cli.py",
+        "core/builder/tests/test_bundle_reader.py",
         "core/builder/tests/test_bundle_writer.py",
         "core/builder/tests/test_byok.py",
         "core/builder/tests/test_graph_transform.py",