diff --git a/.gitignore b/.gitignore
index eaa61537..7b64dfd6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,7 +8,6 @@ build/
 
 node_modules/
 public/
-.tox/
 tmp/
 
 *.sqlite3
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 511671ad..03c1075e 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -54,25 +54,12 @@ Note that `OPTUNA_DASHBOARD_DEBUG=1` makes the server will automatically restart
 
 ## Running tests, lint checks and formatters
 
-### Run all tests and lint checks
-
-```
-$ tox -e ALL
-```
-
 ### Running Python unit tests
 
 ```
 $ python -m unittest
 ```
 
-or
-
-```
-$ pip install tox
-$ tox -e py39
-```
-
 ### Running visual regression tests using pyppeteer
 
 Please run following commands, then check screenshots in `tmp/` directory.
@@ -94,13 +81,6 @@ $ isort . --check
 $ mypy optuna_dashboard python_tests
 ```
 
-or
-
-```
-$ pip install tox
-$ tox -e flake8 -e black -e mypy
-```
-
 ### Auto-formatting TypeScript files (by prettier)
 
 ```