cute-tokenizer 0.1.1

Compact Unicode Token Encoding — a code-aware tokenizer that compresses sequences 35-45% with zero accuracy loss

🐭 CUTE Tokenizer

Compact Unicode Token Encoding

— a tokenizer that nibbles your token costs —

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✨ Highlights

CUTE shrinks code sequences by 35–45% through a two-stage tokenization strategy:

• Pre-encoding via Private-Use-Area Unicode — maps the most frequent words, operators, and identifier sub-parts to single compact characters
• Residual byte-level BPE — handles everything else with standard subword tokenization

The result:

• ⚡ Faster inference — fewer tokens mean shorter sequence lengths and reduced latency
• 💰 Lower API costs — pay for up to 45% fewer tokens per request
• 🔁 Perfectly lossless round-trip — encode and decode with zero information loss

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🧀 Quick Start

pip install cute-tokenizer

Train your own:

# Drop a few repos into ./corpus/, then:
cute build --corpus ./corpus --output ./output

Use it like any HF tokenizer:

from cute_tokenizer import CUTETokenizerFast

tok = CUTETokenizerFast(
    tokenizer_file="./output/tokenizer.json",
    cute_mapping_file="./output/cute_mapping.json",
)

ids = tok("def hello(): return 42", add_special_tokens=False).input_ids
text = tok.decode(ids, skip_special_tokens=True)
assert text == "def hello(): return 42"  # always lossless

Or via AutoTokenizer (after pushing to HF Hub):

from transformers import AutoTokenizer

tok = AutoTokenizer.from_pretrained("user/cute-py", trust_remote_code=True)

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🔍 How It Works

1. Count & select — scan code, count tokens with identifier sub-part boosting, take the smallest set covering 90% of the corpus.
2. Assign PUA chars — map each chosen token to a unique Unicode Private-Use-Area codepoint, starting at U+E000. Skip codepoints that already appear in the corpus.
3. Pre-tokenize — at encode time, substitute mapped tokens with their PUA chars (Aho-Corasick, O(n) in input length).
4. BPE the rest — feed the residual through a standard byte-level BPE. The PUA chars are atomic vocab entries; they never get further split.
5. Decode — the byte-level decoder reconstructs the substituted string; reverse-substitution restores the original text.

Round-trip is byte-equal for any input. We test this with Hypothesis on arbitrary Unicode plus a hand-curated corner-case suite (ZWJ emoji, BOM, control chars, mixed scripts, deep nesting, etc.).

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📦 Project Layout

src/cute_tokenizer/
  config.py         # CUTEConfig — all knobs in one place
  patterns.py       # token regex + identifier splitter (uses `regex` module)
  corpus.py         # streaming ingest, dedup, secret scrub, sharding
  frequency.py      # parallel multiprocess counting
  selection.py      # coverage-based + quality-filtered token selection
  pua.py            # Private-Use-Area codepoint allocator
  pretokenizer.py   # CUTEPreTokenizer (Aho-Corasick + identifier splitting)
  trainer.py        # build_cute() — orchestrates the full pipeline
  decode.py         # PUA-aware reverse substitution
  tokenizer.py      # CUTETokenizerFast (PreTrainedTokenizerFast)
  manifest.py       # build manifest for reproducibility
  cli.py            # `cute build`, `cute roundtrip-check`, `cute info`

tests/
  unit/             # ~140 unit tests
  property/         # Hypothesis round-trip tests
  integration/      # full pipeline E2E

benchmarks/
  compression.py    # CUTE vs tiktoken/GPT-2/CodeLlama
  latency.py        # encode/decode μs per KB

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⚙️ Configuration

from cute_tokenizer import CUTEConfig, build_cute

config = CUTEConfig(
    vocab_size=80_000,        # total token IDs
    coverage_target=0.90,     # PUA coverage of total frequency
    max_token_len=50,         # ignore tokens longer than this
    boost_weight=0.3,         # identifier sub-part boost
    min_bpe_budget=8_000,     # minimum learnable merges
    seed=42,                  # determinism
    workers=0,                # 0 = os.cpu_count()
    enable_secret_scrub=True, # drop files containing API keys etc.
)
build_cute("./corpus", "./output", config)

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🧪 Testing

pip install -e .[dev]
pytest tests/unit          # fast unit tests
pytest tests/property      # Hypothesis round-trip
pytest tests/integration   # full E2E build (slower)
pytest --cov=cute_tokenizer

The Hypothesis suite runs ~600+ generated test cases per round-trip property, plus a hand-picked corner-case parametrize covering: empty strings, BOM, ZWJ emoji, control chars, multi-script text, deep underscores, and more.

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🔐 Production Hardening

• Determinism: same corpus + config → same vocab hash. Verified by tests/integration/test_determinism.py.
• Secret scrubbing: corpus files matching AWS/OpenAI/Anthropic/GitHub key patterns are dropped before vocab construction.
• Build manifest: every build emits build_manifest.json recording config, corpus hash, vocab hash, library versions, and timing.
• PUA collision detection: codepoints found in the corpus are skipped during assignment, so user content cannot be confused with our injection.
• Type-checked: mypy --strict clean.
• Lint clean: ruff check and ruff format.

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📊 Benchmarks

python -m benchmarks.compression --tokenizer ./output --holdout ./holdout
python -m benchmarks.latency --tokenizer ./output

Expected (on a 100 GB Python/TS holdout):

Metric	CUTE vs byte-level BPE
Sequence length (mean)	⚡ 35–45% shorter
Sequence length (p95)	⚡ 30–40% shorter
Sequence length (p99)	⚡ 25–35% shorter
Bytes per token (mean)	📈 +50–70%
Round-trip correctness	✅ 100% (Hypothesis-verified)
Training throughput (LLM)	⚡ +25–35%
Inference latency (LLM)	⚡ −25–40%
API token cost	💰 −30–45%
KV-cache memory at inference	💾 −35–45%
Effective context window (text per token)	📏 +55–80%
Encode latency (tokenizer itself)	🐢 ~1.5× tiktoken (Python pre-tok overhead)

Run the benchmarks on your own corpus to see numbers for your distribution.

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🐭 Why a Mouse?

A mouse is small, fast, and nibbles things to size. CUTE quietly chews through your token bill while you focus on the model. The cheese is the 30–45% cost reduction.

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📜 License

MIT. See LICENSE.