diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index dd29ea5..43c2da4 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -11,7 +11,7 @@ exclude: >
 repos:
 
   - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v4.3.0
+    rev: v4.5.0
     hooks:
     - id: check-json
     - id: check-yaml
@@ -24,17 +24,17 @@ repos:
     - id: isort
 
   - repo: https://github.com/psf/black
-    rev: 22.6.0
+    rev: 23.10.0
     hooks:
     - id: black
 
   - repo: https://github.com/PyCQA/flake8
-    rev: 5.0.2
+    rev: 6.1.0
     hooks:
     - id: flake8
       additional_dependencies: [flake8-bugbear~=22.7]
 
   - repo: https://github.com/pre-commit/mirrors-mypy
-    rev: v0.971
+    rev: v1.6.1
     hooks:
     - id: mypy
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..4bca864
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,15 @@
+# Contributing
+
+`sphinx-external-toc` is part of the executablebooks project, who also are responsible for `jupyter-book`.
+
+We're excited you're here and want to contribute.
+
+The Jupyter Book project is run by a community of people like you, we'd love to have you
+help out!
+
+Please take a look at the [Jupyter Book contributor guide](https://jupyterbook.org/en/stable/contribute/intro.html)
+which steps you through the codebase and how to contribute to this project.
+If you have any questions that aren't answered there, please let us know by
+[opening an issue][link_issues]!
+
+Thank you for you interest in contributing ✨
diff --git a/sphinx_external_toc/events.py b/sphinx_external_toc/events.py
index 522b7b8..dc57ea1 100644
--- a/sphinx_external_toc/events.py
+++ b/sphinx_external_toc/events.py
@@ -220,7 +220,6 @@ def insert_toctrees(app: Sphinx, doctree: nodes.document) -> None:
     node_list: List[nodes.Element] = []
 
     for toctree in doc_item.subtrees:
-
         subnode = toctree_node()
         subnode["parent"] = app.env.docname
         subnode.source = doctree["source"]
@@ -245,13 +244,10 @@ def insert_toctrees(app: Sphinx, doctree: nodes.document) -> None:
         wrappernode.append(subnode)
 
         for entry in toctree.items:
-
             if isinstance(entry, UrlItem):
-
                 subnode["entries"].append((entry.title, entry.url))
 
             elif isinstance(entry, FileItem):
-
                 child_doc_item = site_map[entry]
                 docname = str(entry)
                 title = child_doc_item.title
@@ -326,13 +322,18 @@ def ensure_index_file(app: Sphinx, exception: Optional[Exception]) -> None:
         exception is not None
         or "html" not in app.builder.format
         or app.config.master_doc == "index"
-        # TODO rewrite the redirect if master_doc has changed since last build
+        # TODO: rewrite the redirect if master_doc has changed since last build
         or index_path.exists()
     ):
         return
+
     root_name = remove_suffix(app.config.master_doc, app.config.source_suffix)
-    # TODO the other way to do this would be to
-    # simply copy the contents of the root file? (this method was taken from jupyter-book)
-    redirect_text = f'<meta http-equiv="Refresh" content="0; url={root_name}.html" />\n'
+
+    if app.builder.name == "html":
+        redirect_url = f"{root_name}.html"
+    elif app.builder.name == "dirhtml":
+        redirect_url = f"{root_name}/index.html"
+
+    redirect_text = f'<meta http-equiv="Refresh" content="0; url={redirect_url}" />\n'
     index_path.write_text(redirect_text, encoding="utf8")
     logger.info("[etoc] missing index.html written as redirect to '%s.html'", root_name)
diff --git a/sphinx_external_toc/parsing.py b/sphinx_external_toc/parsing.py
index 8e313a1..717b9fa 100644
--- a/sphinx_external_toc/parsing.py
+++ b/sphinx_external_toc/parsing.py
@@ -193,7 +193,6 @@ def _parse_doc_item(
 
     toctrees = []
     for toc_idx, toc_data in enumerate(subtrees_data):
-
         toc_path = path if shorthand_used else f"{path}{toc_idx}/"
 
         if not (isinstance(toc_data, Mapping) and items_key in toc_data):
@@ -209,7 +208,6 @@ def _parse_doc_item(
         # generate items list
         items: List[Union[GlobItem, FileItem, UrlItem]] = []
         for item_idx, item_data in enumerate(items_data):
-
             if not isinstance(item_data, Mapping):
                 raise MalformedError(
                     f"entry not a mapping type @ '{toc_path}{items_key}/{item_idx}'"
diff --git a/sphinx_external_toc/tools.py b/sphinx_external_toc/tools.py
index 0d77ae6..d3b9e1a 100644
--- a/sphinx_external_toc/tools.py
+++ b/sphinx_external_toc/tools.py
@@ -59,7 +59,6 @@ def create_site_from_toc(
 
     # create files
     for docname in chain(site_map, additional_files):
-
         # create document
         filename = docname
         if not any(docname.endswith(ext) for ext in {".rst", ".md"}):
diff --git a/tests/test_tools.py b/tests/test_tools.py
index 4d77673..c335ceb 100644
--- a/tests/test_tools.py
+++ b/tests/test_tools.py
@@ -26,7 +26,6 @@ def test_file_to_sitemap(path: Path, tmp_path: Path, data_regression):
 
 
 def test_create_site_map_from_path(tmp_path: Path, data_regression):
-
     # create project files
     files = [
         "index.rst",