1.Codeforces

creator: Mike Mirzayanov

📋 Tools for codeforces:

1. Codeforces Visualizer »»»»»👨‍💻 sjsakib
2. code-drills »»»»»👨‍💻 Balajiganapathi
3. Codeshows »»»»»👨‍💻 surya1231
4. cfladders »»»»»👨‍💻 srijan_de
5. Competitive Companion(Chrome Extension) »»»»»👨‍💻 Jasperr
6. CF-Predictor(Chrome/Firefox/Opera Extension) »»»»»👨‍💻Wsl_F
7. Synapse0 (Only for Bangladesh)
8. Upsolve »»»»»👨‍💻 zenolus
9. DYNAMIC A2OJ »»»»»👨‍💻 subodhk

2. AtCoder

creator: Naohiro Takahashi , Makoto Soejima

📋 Tools for atcoder:

1. kenkoooo »»»»»👨‍💻 kenkoooo
2. Competitive Companion(Chrome Extension)»»»»»👨‍💻 Jasperr
3. Official AtCoder(Youtube Channel)
4. Atcoder-scores »»»»»👨‍💻 Shrimp

3. Uva Online Judge

creator: Miguel Ángel Revilla

📋 Tools for uva:

1. luckycat
2. uHunt »»»»»👨‍💻felix_halim
3. Competitive Companion(Chrome Extension)»»»»»👨‍💻 Jasperr
4. udebug

4. Toph

creator : Furqan Software

📋 Tools for toph:

1. Competitive Companion(Chrome Extension)»»»»»👨‍💻 Jasperr
2. udebug

5. Light OJ

creator : Jane Alam Jan

📋 Tools for lightoj:

1. Competitive Companion(Chrome Extension)»»»»»👨‍💻 Jasperr
2. udebug

6. CodeChef

creator : Bhavin Turakhia

📋 Tools for codechef:

1. Competitive Companion(Chrome Extension)»»»»»👨‍💻 Jasperr

7. CSES Problem Set

creator : Antti Laaksonen

📋 Tools for cses:

1. Competitive Programmer’s Handbook(pdf) »»»»»👨‍💻pllk