---
license: cc-by-4.0
task_categories:
- tabular-regression
language:
- en
tags:
- chess
- lichess
- stockfish
- position-evaluation
- game-ai
size_categories:
- 100M<n<1B
---

# Lichess Chess Positions: ML-Ready Deduplicated Evaluations

## Dataset Description

A curated dataset of **316,072,343 unique chess positions** with Stockfish evaluations, optimized for training neural networks. This is a deduplicated, ML-ready version of the [Lichess evaluation database](https://database.lichess.org/#evals).

### Why This Dataset?

While Lichess provides deduplicated evaluations in JSONL.zst format, and HuggingFace hosts the full (non-deduplicated) version, this dataset offers:

**Unique advantages:**
- ✅ Deduplicated (like Lichess source)
- ✅ Parquet format (5-10x faster loading than JSONL.zst)
- ✅ Split into 10 manageable parts (easy incremental downloads)
- ✅ Optimized for ML (removed unnecessary columns)
- ✅ 80% smaller than non-deduplicated version

**Comparison:**
| Source | Duplicates | Format | Size | Splits |
|--------|-----------|--------|------|--------|
| [Lichess DB](https://database.lichess.org/#evals) | None | JSONL.zst | \~17GB (\~83GB decompressed) | 1 file |
| [HF Lichess](https://huggingface.co/datasets/Lichess/chess-position-evaluations) | Yes (784M rows) | Parquet | 30GB+ | 16 parts |
| **This dataset** | None (316M rows) | Parquet | ~7GB | 10 parts |

Perfect for researchers who want deduplicated data without decompressing 80GB+ JSONL.zst files.

## Dataset Structure

### Data Instance

One row of the dataset looks like this:

```json
{
  "fen": "2bq1rk1/pr3ppn/1p2p3/7P/2pP1B1P/2P5/PPQ2PB1/R3R1K1 w - -",
  "depth": 36,
  "cp": 311,
  "mate": null
}
```

### Data Fields

| Field | Type | Description |
|-------|------|-------------|
| `fen` | string | Chess position in [FEN notation](https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation) (pieces, active color, castling rights, en passant) |
| `depth` | int | Search depth reached by Stockfish engine |
| `cp` | int | Centipawn evaluation (-∞ to +∞). `null` if mate is certain |
| `mate` | int | Moves until mate. `null` if mate is not certain |

### Data Splits

The dataset is split into 10 equally-sized parts (~32M positions each) for convenient downloading:

```python
from datasets import load_dataset

# Load full dataset (all 10 parts)
dataset = load_dataset("mateuszgrzyb/lichess-stockfish-normalized", split="train")

# Or load specific percentage (faster download)
dataset = load_dataset("mateuszgrzyb/lichess-stockfish-normalized", split="train[:10%]")

# Or load by number of examples
dataset = load_dataset("mateuszgrzyb/lichess-stockfish-normalized", split="train[:1000000]")
```

## Dataset Creation

### Source Data

Original data: [Lichess evaluation database](https://database.lichess.org/#evals)

- **Source**: Lichess analysis board
- **Evaluator**: Stockfish (various versions and depths)
- **Collection**: Produced by Lichess users running Stockfish in browser during analysis
- **Update frequency**: Monthly (last updated: November 2025)

### Preprocessing Pipeline

The preprocessing was performed as part of the [Searchless Chess project](https://github.com/mateuszgrzyb-pl/searchless-chess):

1. **Data Loading**: Loaded in parts de-normalized posiotions with evaluations `Lichess/chess-position-evaluations` (~37GB)
2. **Deduplication**: For each unique FEN, retained only the evaluation with maximum `depth`
   - Original: 784M rows with duplicates
   - After dedup: 316M unique positions
3. **Column removal**: Removed `line` and `knodes` fields (not needed for position evaluation)
4. **Format conversion**: JSONL (original file in Lichess DataBase) → Parquet (faster I/O for ML workflows)
5. **Partitioning**: Split into 10 equal parts for manageable downloads

**Size reduction**: ~83GB (decompressed JSONL) | ~37GB (Parquet) → ~7GB (deduplicated Parquet) = **over 80% reduction**

### Quality Metrics

- **Unique positions**: 316,072,343
- **Average file size**: ~650MB per part

## Usage Example

### Basic Loading

```python
from datasets import load_dataset

# Load full dataset
dataset = load_dataset("mateuszgrzyb/lichess-stockfish-normalized", split="train")

# Access data
print(f"Total: {len(dataset)}")
print(dataset[0])
```

### Incremental Loading (Memory-Efficient)

```python
from datasets import load_dataset

# Load one part at a time
for i in range(10):
    part = load_dataset(
        "mateuszgrzyb/lichess-stockfish-normalized",
        split=f"train[{i*10}%:{(i+1)*10}%]"
    )
    # Process part...
    train_on_part(part)
```

## Citation

If you use this dataset in your research, please cite:

```bibtex
@dataset{grzyb2025lichess,
  author = {Grzyb, Mateusz},
  title = {Lichess Chess Positions: ML-Ready Deduplicated Evaluations},
  year = {2025},
  publisher = {Hugging Face},
  howpublished = {\url{https://huggingface.co/datasets/mateuszgrzyb/lichess-stockfish-normalized}}
}
```

And cite the original Lichess database:

```bibtex
@misc{lichess2024database,
  author = {Lichess},
  title = {Lichess Elite Database},
  year = {2024},
  url = {https://database.lichess.org}
}
```

## Related Resources

- 📂 **Project Repository**: [Searchless Chess on GitHub](https://github.com/mateuszgrzyb-pl/searchless-chess)
- 📄 **Inspiration**: [Grandmaster-Level Chess Without Search](https://arxiv.org/abs/2402.04494) (DeepMind, 2024)
- ♟️ **Original Dataset**: [Lichess Evaluation Database](https://database.lichess.org/#evals)
- 🤗 **Non-Deduplicated Version**: [Lichess/chess-position-evaluations](https://huggingface.co/datasets/Lichess/chess-position-evaluations)

## License

This dataset is licensed under **CC BY 4.0**.

Original data from [Lichess](https://database.lichess.org/#evals) is licensed under CC0 1.0 (Public Domain).

## Dataset Curator

Created by **Mateusz Grzyb** as part of the [Searchless Chess project](https://github.com/mateuszgrzyb-pl/searchless-chess).


## Changelog

**v1.0.0** (November 2025)
- Initial release
- 316M deduplicated positions
- 10-part split in Parquet format

---

*Dataset last updated: November 2025*