NeuSpell is an open-source toolkit for context sensitive spelling correction in English. This toolkit comprises of 10 spell checkers, with evaluations on naturally occurring mis-spellings from multiple (publicly available) sources. To make neural models for spell checking context dependent, (i) we train neural models using spelling errors in context, synthetically constructed by reverse engineering isolated mis-spellings; and (ii) use richer representations of the context.This toolkit enables NLP practitioners to use our proposed and existing spelling correction systems, both via a simple unified command line, as well as a web interface. Among many potential applications, we demonstrate the utility of our spell-checkers in combating adversarial misspellings.

Command line usage

You can also find this quick-start code snippet in the file

""" load spell checkers """
from neuspell import BertsclstmChecker, SclstmChecker
checker = SclstmChecker()
checker = checker.add_("elmo", at="input")

""" spell correction """
checker.correct(["I luk foward to receving your reply"])
# → ["I look forward to receiving your reply"]
# → "Found 450 mistakes in 322 lines, total_lines=350"

""" evaluation of models """
checker.evaluate(clean_file="bea60k.txt", corrupt_file="bea60k.noise.txt")
# → data size: 63044
# → total inference time for this data is: 998.13 secs
# → total token count: 1032061
# → confusion table: corr2corr:940937, corr2incorr:21060,
#                    incorr2corr:55889, incorr2incorr:14175
# → accuracy is 96.58%
# → word correction rate is 79.76%

""" fine-tuning on domain specific dataset """
checker.finetune(clean_file="clean.txt", corrupt_file="corrupt.txt")


Time per
(in milliseconds)
Aspell 48.7 7.3*
Jamspell 68.9 2.6*
CNN-LSTM 75.8 4.2
SC-LSTM 76.7 2.8
Nested-LSTM 77.3 6.4
BERT 79.1 7.1
SC-LSTM plus ELMO (at input) 79.8 15.8
SC-LSTM plus ELMO (at output) 78.5 16.3
SC-LSTM plus BERT (at input) 77.0 6.7
SC-LSTM plus BERT (at output) 76.0 7.2

Performance of different correctors in the NeuSpell toolkit on the BEA-60K dataset with real-world spelling mistakes.
∗ indicates evaluation on a CPU (for others we use a GeForce RTX 2080 Ti GPU).

Pretrained models


Run the following to download checkpoints of all neural models

cd data/checkpoints

See data/checkpoints/ for more details. You can alternatively choose to download only selected models' checkpoints.


Download datasets

Run the following to download datasets

cd data/traintest

See data/traintest/ for more details.

Synthetic Training Dataset Creation

The toolkit offers 4 kinds of noising strategies to generate synthetic parallel training data to train neural models for spell correction.

  • Word Replacement
  • Probabilistic Replacement
  • A combination of Word Replacement and Probabilistic Replacement

Train files are dubbed with names .random, .word, .prob, .probword respectively. For each strategy, we noise ∼20% of the tokens in the clean corpus. We use 1.6 Million sentences from the One billion word benchmark dataset as our clean corpus.

Potential applications for practitioners

  • Defenses against adversarial attacks in NLP
    • example implementation available in folder ./applications/Adversarial-Misspellings
  • Improving OCR text correction systems
  • Improving grammatical error correction systems
  • Improving Intent/Domain classifiers in conversational AI
  • Spell Checking in Collaboration and Productivity tools


The toolkit was developed in python 3.7.

Required packages can be installed as:

pip install -r requirements.txt

The code requires spacy models which can be downloaded as:

python -m spacy download en_core_web_sm

Requirements for Aspell checker:

tar -C . -xvf aspell-python-py3-1.15.tar.bz2
cd aspell-python-py3-1.15
python install

Requirements for Jamspell checker:

sudo apt-get install -y swig3.0
wget -P ./
tar xf ./en.tar.gz --directory ./


      title={NeuSpell: A Neural Spelling Correction Toolkit}, 
      author={Sai Muralidhar Jayanthi and Danish Pruthi and Graham Neubig},