diff --git a/backend/app/api/tags.py b/backend/app/api/tags.py
index c44cdd9..64f16bf 100644
--- a/backend/app/api/tags.py
+++ b/backend/app/api/tags.py
@@ -8,6 +8,7 @@ from ..extensions import get_session
 from ..models import Tag, TagKind
 from ..models.tag_allowlist import TagAllowlist
 from ..services.bulk_tag_service import BulkTagService
+from ..services.series_service import SeriesError, SeriesService
 from ..services.tag_directory_service import TagDirectoryService
 from ..services.tag_service import (
     TagMergeConflict,
@@ -27,7 +28,9 @@ def _coerce_kind(raw: str | None) -> TagKind | None:
         return None
 
 
-def _parse_bulk_ids(body) -> tuple[list[int] | None, tuple | None]:
+def _parse_bulk_ids(
+    body, *, max_ids: int = 200
+) -> tuple[list[int] | None, tuple | None]:
     """Returns (image_ids, error). error is (json, status) or None."""
     if not body or "image_ids" not in body:
         return None, (jsonify({"error": "image_ids required"}), 400)
@@ -44,9 +47,9 @@ def _parse_bulk_ids(body) -> tuple[list[int] | None, tuple | None]:
             jsonify({"error": "image_ids must be integers"}),
             400,
         )
-    if len(ids) > 200:
+    if len(ids) > max_ids:
         return None, (
-            jsonify({"error": "selection too large (max 200)"}),
+            jsonify({"error": f"selection too large (max {max_ids})"}),
             400,
         )
     return ids, None
@@ -282,3 +285,82 @@ async def bulk_remove_tag():
         )
         await session.commit()
     return jsonify({"removed_count": removed})
+
+
+def _series_err(exc: SeriesError):
+    msg = str(exc)
+    status = 404 if ("not found" in msg or "not a series" in msg) else 400
+    return jsonify({"error": msg}), status
+
+
+@tags_bp.route("/series/<int:tag_id>/pages", methods=["GET"])
+async def series_pages(tag_id: int):
+    async with get_session() as session:
+        try:
+            data = await SeriesService(session).list_pages(tag_id)
+        except SeriesError as exc:
+            return _series_err(exc)
+    return jsonify(data)
+
+
+@tags_bp.route("/series/<int:tag_id>/pages", methods=["POST"])
+async def series_add(tag_id: int):
+    body = await request.get_json()
+    ids, err = _parse_bulk_ids(body, max_ids=500)
+    if err:
+        return err
+    async with get_session() as session:
+        try:
+            n = await SeriesService(session).add_images(tag_id, ids)
+        except SeriesError as exc:
+            return _series_err(exc)
+        await session.commit()
+    return jsonify({"added_count": n})
+
+
+@tags_bp.route("/series/<int:tag_id>/pages/remove", methods=["POST"])
+async def series_remove(tag_id: int):
+    body = await request.get_json()
+    ids, err = _parse_bulk_ids(body, max_ids=500)
+    if err:
+        return err
+    async with get_session() as session:
+        try:
+            n = await SeriesService(session).remove_images(tag_id, ids)
+        except SeriesError as exc:
+            return _series_err(exc)
+        await session.commit()
+    return jsonify({"removed_count": n})
+
+
+@tags_bp.route("/series/<int:tag_id>/reorder", methods=["POST"])
+async def series_reorder(tag_id: int):
+    body = await request.get_json()
+    ids, err = _parse_bulk_ids(body, max_ids=500)
+    if err:
+        return err
+    async with get_session() as session:
+        try:
+            await SeriesService(session).reorder(tag_id, ids)
+        except SeriesError as exc:
+            return _series_err(exc)
+        await session.commit()
+    return jsonify({"ok": True})
+
+
+@tags_bp.route("/series/<int:tag_id>/cover", methods=["POST"])
+async def series_cover(tag_id: int):
+    body = await request.get_json()
+    if not body or "image_id" not in body:
+        return jsonify({"error": "image_id required"}), 400
+    try:
+        image_id = int(body["image_id"])
+    except (TypeError, ValueError):
+        return jsonify({"error": "image_id must be an integer"}), 400
+    async with get_session() as session:
+        try:
+            await SeriesService(session).set_cover(tag_id, image_id)
+        except SeriesError as exc:
+            return _series_err(exc)
+        await session.commit()
+    return jsonify({"ok": True})
diff --git a/tests/test_api_series.py b/tests/test_api_series.py
new file mode 100644
index 0000000..5f70f6b
--- /dev/null
+++ b/tests/test_api_series.py
@@ -0,0 +1,72 @@
+import pytest
+
+from backend.app import create_app
+
+pytestmark = pytest.mark.integration
+
+
+@pytest.fixture
+async def app():
+    return create_app()
+
+
+@pytest.fixture
+async def client(app):
+    async with app.test_client() as c:
+        yield c
+
+
+async def _series(client, name="Vol"):
+    r = await client.post("/api/tags", json={"name": name, "kind": "series"})
+    return (await r.get_json())["id"]
+
+
+@pytest.mark.asyncio
+async def test_pages_404_for_non_series(client):
+    r = await client.post("/api/tags", json={"name": "g", "kind": "general"})
+    gid = (await r.get_json())["id"]
+    resp = await client.get(f"/api/series/{gid}/pages")
+    assert resp.status_code == 404
+
+
+@pytest.mark.asyncio
+async def test_pages_empty_shape(client):
+    sid = await _series(client, "Empty")
+    resp = await client.get(f"/api/series/{sid}/pages")
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert body["series"]["id"] == sid
+    assert body["pages"] == []
+
+
+@pytest.mark.asyncio
+async def test_add_requires_ids(client):
+    sid = await _series(client, "NoIds")
+    resp = await client.post(f"/api/series/{sid}/pages", json={})
+    assert resp.status_code == 400
+
+
+@pytest.mark.asyncio
+async def test_add_over_cap_400(client):
+    sid = await _series(client, "Cap")
+    resp = await client.post(
+        f"/api/series/{sid}/pages",
+        json={"image_ids": list(range(1, 502))},
+    )
+    assert resp.status_code == 400
+
+
+@pytest.mark.asyncio
+async def test_reorder_mismatch_400(client):
+    sid = await _series(client, "Re")
+    resp = await client.post(
+        f"/api/series/{sid}/reorder", json={"image_ids": [1, 2, 3]}
+    )
+    assert resp.status_code == 400
+
+
+@pytest.mark.asyncio
+async def test_cover_requires_image_id(client):
+    sid = await _series(client, "Cov")
+    resp = await client.post(f"/api/series/{sid}/cover", json={})
+    assert resp.status_code == 400