Grammarly vs Codex (OpenAI)
Which one should you pick? Here's the full breakdown.
Grammarly
AI writing assistant that catches errors everywhere you type -- now with full AI rewriting
Codex (OpenAI)
OpenAI's cloud-based coding agent -- runs parallel tasks, proposes PRs, and lives inside ChatGPT
Powered by GPT-5.3-Codex / GPT-5.4
| Category | Grammarly | Codex (OpenAI) |
|---|---|---|
| Ease of Use | 10.0 | 8.0 |
| Output Quality | 7.0 | 8.0 |
| Value | 7.0 | 8.0 |
| Features | 8.0 | 9.0 |
| Overall | 8.0 | 8.3 |
Pricing Comparison
| Feature | Grammarly | Codex (OpenAI) |
|---|---|---|
| Free Tier | Yes | Yes |
| Starting Price | $0 | $0 |
Benchmark Head-to-Head
GPT-5.3-Codex benchmarks — Grammarly has no published benchmarks
| Benchmark | Description | Score |
|---|---|---|
| SWE-bench | Real GitHub issue fixing | 72% |
| HumanEval | Python code generation | 95% |
Which Should You Pick?
Pick Grammarly if...
- ✓Easier to use (10 vs 8)
Non-native English speakers, professionals who write lots of emails, and anyone who wants a passive grammar net running in the background. It catches things you'd miss.
Visit GrammarlyPick Codex (OpenAI) if...
- ✓Higher output quality (8 vs 7)
- ✓Better value for money (8/10)
- ✓More features (9 vs 8)
Developers already paying for ChatGPT Plus who want a coding agent at no extra cost. Especially good for parallel task execution -- assign multiple bug fixes or feature branches and let Codex work them simultaneously.
Visit Codex (OpenAI)Our Verdict
Codex (OpenAI) edges out Grammarly with a 8.3 vs 8.0 overall score. Both are solid picks, but Codex (OpenAI) has the advantage in output quality.