diff --git a/.github/workflows/tox.yml b/.github/workflows/tox.yml
index 9c0085ed..813d005a 100644
--- a/.github/workflows/tox.yml
+++ b/.github/workflows/tox.yml
@@ -26,14 +26,12 @@ jobs:
             $RUNNER_TOOL_CACHE/Python/*
             ~\AppData\Local\pip\Cache
           key: ${{ runner.os }}-build-${{ matrix.python-version }}
-      - name: install-tox
-        run: python -m pip install --upgrade tox virtualenv setuptools pip
-      - name: run-tox
-        run: tox -e py
-      - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
-        if: matrix.python-version == '3.8' && matrix.os == 'ubuntu-18.04'
-        with:
-          env_vars: OS,PYTHON
-          name: codecov-umbrella
-          fail_ci_if_error: true
+      - name: install-reqs
+        run: |
+          python -m pip install --upgrade tox virtualenv setuptools pip
+          python -m pip install -U -r requirements-dev.txt
+          python -m pip install -e .
+      - name: run-tests
+        run: pytest tests --cov=100
+      - name: run-pyrefly
+        run: pyrefly check nbqa
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index dc8fa082..d6afb1d8 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -42,7 +42,7 @@ repos:
     hooks:
       - id: mypy
         exclude: ^docs/
-        additional_dependencies: [types-setuptools, types-toml]
+        additional_dependencies: [types-setuptools, types-toml, tokenize-rt]
   - repo: https://github.com/asottile/pyupgrade
     rev: v3.19.1
     hooks:
diff --git a/nbqa/__main__.py b/nbqa/__main__.py
index 087eb1d3..c529ec7a 100644
--- a/nbqa/__main__.py
+++ b/nbqa/__main__.py
@@ -460,7 +460,10 @@ def _get_configs(cli_args: CLIArgs, project_root: Path) -> Configs:
         if getattr(cli_args, section) is not None:
             if section == "addopts":
                 # addopts are added to / overridden rather than replaced outright
-                config["addopts"] = (*config["addopts"], *getattr(cli_args, section))
+                config["addopts"] = (  # type: ignore[missing-attribute,unused-ignore]
+                    *config["addopts"],
+                    *getattr(cli_args, section),
+                )
             else:
                 # TypedDict key must be a string literal
                 config[section] = getattr(cli_args, section)  # type: ignore
@@ -767,7 +770,7 @@ def _main(cli_args: CLIArgs, configs: Configs) -> int:
                 for key, i in nb_to_tmp_mapping.items()
                 if key
                 not in (
-                    *saved_sources.failed_notebooks,
+                    *saved_sources.failed_notebooks,  # type: ignore[not-a-type, unused-ignore]
                     *saved_sources.non_python_notebooks,
                 )
             ],
diff --git a/nbqa/path_utils.py b/nbqa/path_utils.py
index 3a5b37d8..6b954d77 100644
--- a/nbqa/path_utils.py
+++ b/nbqa/path_utils.py
@@ -4,7 +4,7 @@
 import os
 import string
 from pathlib import Path
-from typing import Any, Dict, Optional, Tuple
+from typing import Any, Dict, Optional, Tuple, cast
 
 
 def remove_prefix(string_: str, prefix: str) -> str:
@@ -106,7 +106,10 @@ def read_notebook(notebook: str) -> Tuple[Optional[Dict[str, Any]], Optional[boo
         config = None
 
     try:
-        md_content = jupytext.jupytext.read(notebook, config=config)
+        # jupytext isn't typed unfortunately
+        md_content = cast(  # type: ignore[missing-attribute,unused-ignore]
+            Any, jupytext.jupytext.read(notebook, config=config)
+        )
     except:  # noqa: E72a  # pylint: disable=bare-except
         return None, None
 
diff --git a/nbqa/replace_source.py b/nbqa/replace_source.py
index 94588f63..48da39a0 100644
--- a/nbqa/replace_source.py
+++ b/nbqa/replace_source.py
@@ -58,7 +58,7 @@ def _restore_semicolon(
         for idx, token in tokenize_rt.reversed_enumerate(tokens):
             if not token.src.strip(" \n") or token.name == "COMMENT":
                 continue
-            tokens[idx] = token._replace(src=token.src + ";")
+            tokens[idx] = token._replace(src=token.src + ";")  # type: ignore[missing-attribute,unused-ignore]
             break
         source = tokenize_rt.tokens_to_src(tokens)
     return source
@@ -226,7 +226,9 @@ def _write_notebook(
 
         for cell in notebook_json["cells"]:
             cell["source"] = "".join(cell["source"])
-        jupytext.jupytext.write(notebook_json, temp_notebook, config=config)
+        jupytext.jupytext.write(  # type: ignore[missing-attribute,unused-ignore]
+            notebook_json, temp_notebook, config=config
+        )
 
 
 def mutate(  # pylint: disable=too-many-locals,too-many-arguments
diff --git a/nbqa/save_code_source.py b/nbqa/save_code_source.py
index 5de39e99..352a091b 100644
--- a/nbqa/save_code_source.py
+++ b/nbqa/save_code_source.py
@@ -328,7 +328,7 @@ def _has_trailing_semicolon(src: str) -> tuple[str, bool]:
         if not token.src.strip(" \n") or token.name == "COMMENT":
             continue
         if token.name == "OP" and token.src == ";":
-            tokens[idx] = token._replace(src="")
+            tokens[idx] = token._replace(src="")  # type: ignore[missing-attribute,unused-ignore]
             trailing_semicolon = True
         break
     if not trailing_semicolon:
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 45632468..4c8569c9 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -12,6 +12,7 @@ pre-commit
 pre-commit-hooks
 pydocstyle
 pylint
+pyrefly
 pytest
 pytest-cov
 pytest-randomly
diff --git a/tox.ini b/tox.ini
index c596dc3c..32c21179 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,5 +1,5 @@
 [tox]
-envlist = py{38,39,310,311}, docs, docs-links
+envlist = pyrefly, py{38,39,310,311}, docs, docs-links
 
 [testenv:docs]
 deps = -rdocs/requirements-docs.txt
@@ -19,3 +19,9 @@ commands =
     coverage run -m pytest {posargs:tests -vv -W error}
     coverage xml
     coverage report --fail-under 100 --show-missing
+
+[testenv:pyrefly]
+deps =
+    -rrequirements-dev.txt
+commands =
+    pyrefly check nbqa