diff --git a/surfsense_backend/tests/unit/services/okf/test_serializer.py b/surfsense_backend/tests/unit/services/okf/test_serializer.py
new file mode 100644
index 000000000..157ed44c8
--- /dev/null
+++ b/surfsense_backend/tests/unit/services/okf/test_serializer.py
@@ -0,0 +1,130 @@
+"""OKF serializer/validator self-checks: emitted concepts stay conformant and the
+frontmatter fields consumers rely on (type/title/timestamp) round-trip.
+"""
+
+from datetime import UTC, datetime
+
+from app.db import Document, DocumentType
+from app.services.okf import (
+    ConceptRef,
+    LogEntry,
+    SubdirRef,
+    document_to_concept,
+    folder_to_index,
+    folder_to_log,
+    is_conformant_concept,
+    parse_frontmatter,
+    validate_concept,
+)
+
+
+def _make_document() -> Document:
+    return Document(
+        title="Weekly Sync Notes",
+        document_type=DocumentType.NOTE,
+        document_metadata={"tags": ["team", "meeting"], "url": "https://example.com/n"},
+        updated_at=datetime(2026, 5, 28, 22, 49, 59, tzinfo=UTC),
+    )
+
+
+def test_concept_is_conformant_and_roundtrips() -> None:
+    concept = document_to_concept(_make_document(), body="# Agenda\n\nShip OKF.")
+
+    assert is_conformant_concept(concept)
+
+    frontmatter, error = parse_frontmatter(concept)
+    assert error is None
+    assert frontmatter["type"] == "Note"
+    assert frontmatter["title"] == "Weekly Sync Notes"
+    assert frontmatter["tags"] == ["team", "meeting"]
+    assert frontmatter["resource"] == "https://example.com/n"
+    # timestamp must survive as an ISO-8601 string, not a parsed datetime.
+    assert frontmatter["timestamp"] == "2026-05-28T22:49:59+00:00"
+    assert "# Agenda" in concept
+
+
+def test_type_is_always_present_even_without_metadata() -> None:
+    doc = Document(title="Raw", document_type=DocumentType.CRAWLED_URL)
+    concept = document_to_concept(doc, body="body")
+    frontmatter, error = parse_frontmatter(concept)
+    assert error is None
+    assert frontmatter["type"] == "Web Page"
+    # No source URL / tags available -> those recommended keys are omitted.
+    assert "resource" not in frontmatter
+    assert "tags" not in frontmatter
+
+
+def test_validator_rejects_non_conformant_documents() -> None:
+    assert validate_concept("no frontmatter here")
+    assert validate_concept("---\ntitle: Missing type\n---\nbody")
+
+
+def test_folder_index_groups_by_type_and_lists_subdirs() -> None:
+    index = folder_to_index(
+        concepts=[
+            ConceptRef(title="Orders", filename="orders.md", type="Note", description="x"),
+        ],
+        subdirectories=[SubdirRef(name="tables", description="Table docs")],
+    )
+    assert "# Subdirectories" in index
+    assert "* [tables](tables/index.md) - Table docs" in index
+    assert "# Note" in index
+    assert "* [Orders](orders.md) - x" in index
+
+
+def test_folder_log_lists_concepts_newest_first() -> None:
+    log = folder_to_log(
+        [
+            LogEntry(title="Older", timestamp="2026-01-01T00:00:00+00:00"),
+            LogEntry(title="Newer", timestamp="2026-06-01T00:00:00+00:00"),
+            LogEntry(title="Undated", timestamp=None),
+        ]
+    )
+    assert "# Change Log" in log
+    # Newest dated entry precedes the older one; undated sorts last.
+    assert log.index("Newer") < log.index("Older") < log.index("Undated")
+    assert "* Newer - 2026-06-01T00:00:00+00:00" in log
+
+
+def test_folder_log_is_empty_when_no_entries() -> None:
+    assert folder_to_log([]) == ""
+
+
+def test_export_log_files_synthesized_only_where_docs_live() -> None:
+    from app.services.export_service import _build_log_files
+
+    files = dict(
+        _build_log_files(
+            {
+                "": [LogEntry(title="Root Doc", timestamp="2026-05-01T00:00:00+00:00")],
+                "Research/AI": [LogEntry(title="Nested", timestamp=None)],
+            }
+        )
+    )
+    assert "# Change Log" in files["log.md"]
+    assert "Root Doc" in files["log.md"]
+    assert "Nested" in files["Research/AI/log.md"]
+    # No empty intermediate log: "Research" holds no concepts of its own.
+    assert "Research/log.md" not in files
+
+
+def test_export_index_files_include_root_version_and_ancestors() -> None:
+    from app.services.export_service import _build_index_files
+
+    # A concept nested two levels deep, with no direct docs in the middle dir.
+    files = dict(
+        _build_index_files(
+            {
+                "Research/AI": [
+                    ConceptRef(title="Note", filename="note.md", type="Note")
+                ]
+            }
+        )
+    )
+
+    # Root, the empty intermediate dir, and the leaf all get an index.md so the
+    # hierarchy is fully navigable.
+    assert files["index.md"].startswith('---\nokf_version: "0.1"\n---')
+    assert "* [Research](Research/index.md)" in files["index.md"]
+    assert "* [AI](AI/index.md)" in files["Research/index.md"]
+    assert "* [Note](note.md)" in files["Research/AI/index.md"]