Contamination Detection

Decon identifies documents contaminated with eval instances.

It uses simple token based sampling and counting methods, making it suitable for large datasets. It is deterministic with interpretable results.

Decon can produce contamination reports and cleaned datasets.

Note

🐍 This fork adds Python bindings — the core Rust functionality is unchanged. Skip to Python Quick Start to get started, or see the Architecture section to understand how bindings are structured. For the full Python API signature, see crates/decon-py/src/lib.rs. The goal of this fork is to simply expose the API transparently for python users. Please note, the package currently used by decon is decontaminate, import is import decon. Use pip install decontaminate to install the package to get started.

How Decon Works

Consider a 30GB web dataset in ~/sample-data that includes documents containing evaluation question text.

TRAINING DOC:

"... for θ 30 c i θ i0 4 for θ 90 d i θ is constant for all values of θ the plane face of plano convex lens of focal length 20 cm is silvered this combination is equivalent to the type of mirror and its focal length is a convex f 20 c m b concave f 20 cm in a displacement method using convex lens two images are obtained for a separation of d between ..."

EVAL PROMPT: the plane face of plano convex lens of focal length 20 cm is silvered this combination is equivalent to the type of mirror and its focal length is

EVAL ANSWER: concave f 10 cm

We can identify the contamination locations running decon.

$ decon detect --training-dir ~/sample-data --evals-dir ~/references

Training files 4,487/4,487 [00:02:55/00:00:00] [████████████████████████████████████]

┌───────────────────────────────────────────┐
│     Contamination Detection Results       │
├───────────────────────────────────────────┤
│ Training lines                  5,162,084 │
│ Processing rate                 34 μs/doc │
├───────────────────────────────────────────┤
│ Index building time                38.59s │
│ Detection time                    175.69s │
│ Total time                        214.28s │
├───────────────────────────────────────────┤
│ Contaminated matches                7,699 │
│ Contaminated documents              1,851 │
└───────────────────────────────────────────┘

$ decon review --stats /tmp/decon-295c0cbd

=== TRAINING DOCUMENTS CONTAMINATED BY EVAL SUITE ===
(Each count represents unique training documents that need removal)

  sciq                                  652 │███████████████████████████████████████│
  mmlu                                  278 │█████████████████████                  │
  mmlu_pro                              211 │████████████████                       │
  ai2_arc_easy                           83 │██████                                 │
  super_gpqa                             65 │████                                   │

  ...

Quick Start

Python

pip install decontaminate

import decon

config = decon.Config(
    training_dir="/path/to/training/data",
    evals_dir="/path/to/eval/references",
    report_output_dir="/path/to/output",
)
report_dir = decon.detect(config)

PyPI package is decontaminate, import is import decon.

See crates/decon-py/src/lib.rs for all Config parameters and available functions (detect, review, compare, evals, server, Tokenizer, clean_text).

---

CLI (Rust)

# Clone and build. Requires rust 1.88
git clone https://github.com/allenai/decon
cd decon

# For full set of commands and options, help is available.
cargo run --release -- --help

# List current eval datasets in reference (small default set initially).
cargo run --release -- evals

# Run contamination detection.
cargo run --release -- detect --training-dir tests/fixtures/training/

# Create a clean copy (contaminated documents removed) of your dataset.
cargo run --release -- detect --training-dir tests/fixtures/training/ --purify

# Review report output. A decon detect run will report an output directory.
cargo run --release -- review /tmp/decon-output-directory

Sensible defaults are provided for decon parameters, with a single contamination_score_threshold that can be adjusted to desired sensitivity. Experimenting with these parameters on your own dataset and eval reference set is recommended.

Advanced Usage

Preparing Datasets

Training Documents

Decon operates on a directory containing jsonl files.

Each JSON object in the files must contain a field with a string value representing a training document [example].

Eval Suites

Decon runs against a reference set of eval suites that is also expected be a directory containing jsonl files [example].

Decon eval reference files have a normalized format including passage, question, answer keys as well as metadata for reporting. Decon includes tooling to generate reference files from hf datasets.

Eval Reference Set Curation

Three eval suites are included in the eval reference dataset by default, gsm8k, mmlu, and agi_eval.

It's likely you will want to build your own reference set with your evals of interest.

The decon evals command can process an extensible declarative yaml file to normalize huggingface datasets.

To download all the pre-configured evals included in the configuration file, run the following command. This requires python3 with the datasets library installed.

# Review current set of evals in reference
cargo run --release -- evals

# Download and normalize all evals configured in a config file
cargo run --release -- evals --download --config config/evals.yaml

See the Evaluation Dataset Guide for more information on preparing evaluation datasets.

Server

Decon can also be run as a server to facilitate distributing workloads.

# Launch a server
decon server --port 8080

An example orchestration script is provided which demonstrates one approach to batch retrieve a partition of documents, submit documents to the server, poll for job status, and upload reports and clean documents to a new location.

See deployment guide for details.

Reviewing Results

Decon includes tools for qualitative review and basic stats which can be filtered to analyze contamination.

# To qualitatively review individual matches
cargo run --release -- review /my-results-directory

# To see statistics
cargo run --release -- review --stats /my-results-directory

# To review with filters, e.g. specific eval with minimum score
cargo run --release -- review /my-results-directory --eval mmlu --min-score 0.9

# Compare results between different decontamination runs
cargo run --release -- compare /tmp/results-a /tmp/results-b

Decon reports are jsonl files which are ready for analysis beyond the provided tooling.

Architecture

This fork restructures decon as a Rust workspace with three crates:

Crate	Source	Description
decon-core	crates/decon-core/	Core detection engine — pure Rust library (unchanged from upstream)
decon-cli	crates/decon-cli/	Command-line interface built on decon-core
decon-py	crates/decon-py/	Python bindings via PyO3

How Python Bindings Work

The Python bindings are a thin wrapper around decon-core — no detection logic is reimplemented in Python. Key files:

File	Purpose
crates/decon-py/src/lib.rs	PyO3 wrapper classes (PyConfig, PyTokenizer) and functions (detect, clean_text)
crates/decon-py/python/decon/__init__.py	Python module re-exports
crates/decon-py/tests/test_parity.py	Parity tests ensuring Python ↔ Rust equivalence

The detect() function releases the GIL via py.allow_threads(), enabling full utilization of Rayon's parallel processing on all CPU cores.

Building from Source

Rust CLI:

cargo build --release
# Binary at: target/release/decon

Python bindings (requires maturin):

cd crates/decon-py
maturin develop --release
# Or build wheels: maturin build --release

📦 Detailed guide: See doc/building.md for cross-platform builds, troubleshooting, and CI/CD.

Requirements

• Rust: 1.88+ (edition 2024)
• Python: 3.12+ (for bindings)