huggingface-tokenizers

HuggingFace Tokenizers - Fast Tokenization for NLP

Fast, production-ready tokenizers with Rust performance and Python ease-of-use.

When to use HuggingFace Tokenizers

Use HuggingFace Tokenizers when:

• Need extremely fast tokenization (<20s per GB of text)
• Training custom tokenizers from scratch
• Want alignment tracking (token → original text position)
• Building production NLP pipelines
• Need to tokenize large corpora efficiently

Performance:

• Speed: <20 seconds to tokenize 1GB on CPU
• Implementation: Rust core with Python/Node.js bindings
• Efficiency: 10-100× faster than pure Python implementations

Use alternatives instead:

• SentencePiece: Language-independent, used by T5/ALBERT
• tiktoken: OpenAI's BPE tokenizer for GPT models
• transformers AutoTokenizer: Loading pretrained only (uses this library internally)

Quick start

Installation

# Install tokenizers
pip install tokenizers

# With transformers integration
pip install tokenizers transformers

Load pretrained tokenizer

from tokenizers import Tokenizer

# Load from HuggingFace Hub
tokenizer = Tokenizer.from_pretrained("bert-base-uncased")

# Encode text
output = tokenizer.encode("Hello, how are you?")
print(output.tokens)  # ['hello', ',', 'how', 'are', 'you', '?']
print(output.ids)     # [7592, 1010, 2129, 2024, 2017, 1029]

# Decode back
text = tokenizer.decode(output.ids)
print(text)  # "hello, how are you?"

Train custom BPE tokenizer

from tokenizers import Tokenizer
from tokenizers.models import BPE
from tokenizers.trainers import BpeTrainer
from tokenizers.pre_tokenizers import Whitespace

# Initialize tokenizer with BPE model
tokenizer = Tokenizer(BPE(unk_token="[UNK]"))
tokenizer.pre_tokenizer = Whitespace()

# Configure trainer
trainer = BpeTrainer(
    vocab_size=30000,
    special_tokens=["[UNK]", "[CLS]", "[SEP]", "[PAD]", "[MASK]"],
    min_frequency=2
)

# Train on files
files = ["train.txt", "validation.txt"]
tokenizer.train(files, trainer)

# Save
tokenizer.save("my-tokenizer.json")