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Modern spell checking library - accurate, fast, multi-language


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JamSpell is a spell checking library with following features:

  • accurate - it considers words surroundings (context) for better correction
  • fast - near 5K words per second
  • multi-language - it's written in C++ and available for many languages with swig bindings

Colab example

JamSpellPro - check out a new jamspell version with following features

  • Improved accuracy (catboost gradient boosted decision trees candidates ranking model)
  • Splits merged words
  • Pre-trained models for many languages (small, medium, large) for:
    en, ru, de, fr, it, es, tr, uk, pl, nl, pt, hi, no
  • Ability to add words / sentences at runtime
  • Fine-tuning / additional training
  • Memory optimization for training large models
  • Static dictionary support
  • Built-in Java, C#, Ruby support
  • Windows support



Errors Top 7 Errors Fix Rate Top 7 Fix Rate Broken Speed
JamSpell 3.25% 1.27% 79.53% 84.10% 0.64% 4854
Norvig 7.62% 5.00% 46.58% 66.51% 0.69% 395
Hunspell 13.10% 10.33% 47.52% 68.56% 7.14% 163
Dummy 13.14% 13.14% 0.00% 0.00% 0.00% -

Model was trained on 300K wikipedia sentences + 300K news sentences (english). 95% was used for train, 5% was used for evaluation. Errors model was used to generate errored text from the original one. JamSpell corrector was compared with Norvig's one, Hunspell and a dummy one (no corrections).

We used following metrics:

  • Errors - percent of words with errors after spell checker processed
  • Top 7 Errors - percent of words missing in top7 candidated
  • Fix Rate - percent of errored words fixed by spell checker
  • Top 7 Fix Rate - percent of errored words fixed by one of top7 candidates
  • Broken - percent of non-errored words broken by spell checker
  • Speed - number of words per second

To ensure that our model is not too overfitted for wikipedia+news we checked it on "The Adventures of Sherlock Holmes" text:

Errors Top 7 Errors Fix Rate Top 7 Fix Rate Broken Speed (words per second)
JamSpell 3.56% 1.27% 72.03% 79.73% 0.50% 5524
Norvig 7.60% 5.30% 35.43% 56.06% 0.45% 647
Hunspell 9.36% 6.44% 39.61% 65.77% 2.95% 284
Dummy 11.16% 11.16% 0.00% 0.00% 0.00% -

More details about reproducing available in "Train" section.



  1. Install swig3 (usually it is in your distro package manager)

  2. Install jamspell:

pip install jamspell
  1. Download or train language model

  2. Use it:

import jamspell

corrector = jamspell.TSpellCorrector()

corrector.FixFragment('I am the begt spell cherken!')
# u'I am the best spell checker!'

corrector.GetCandidates(['i', 'am', 'the', 'begt', 'spell', 'cherken'], 3)
# (u'best', u'beat', u'belt', u'bet', u'bent', ... )

corrector.GetCandidates(['i', 'am', 'the', 'begt', 'spell', 'cherken'], 5)
# (u'checker', u'chicken', u'checked', u'wherein', u'coherent', ...)


  1. Add jamspell and contrib dirs to your project

  2. Use it:

#include <jamspell/spell_corrector.hpp>

int main(int argc, const char** argv) {

    NJamSpell::TSpellCorrector corrector;

    corrector.FixFragment(L"I am the begt spell cherken!");
    // "I am the best spell checker!"

    corrector.GetCandidates({L"i", L"am", L"the", L"begt", L"spell", L"cherken"}, 3);
    // "best", "beat", "belt", "bet", "bent", ... )

    corrector.GetCandidates({L"i", L"am", L"the", L"begt", L"spell", L"cherken"}, 3);
    // "checker", "chicken", "checked", "wherein", "coherent", ... )
    return 0;

Other languages

You can generate extensions for other languages using swig tutorial. The swig interface file is jamspell.i. Pull requests with build scripts are welcome.


  • Install cmake

  • Clone and build jamspell (it includes http server):

git clone
cd JamSpell
mkdir build
cd build
cmake ..
./web_server/web_server en.bin localhost 8080
  • GET Request example:
$ curl "http://localhost:8080/fix?text=I am the begt spell cherken"
I am the best spell checker
  • POST Request example
$ curl -d "I am the begt spell cherken" http://localhost:8080/fix
I am the best spell checker
  • Candidate example
curl "http://localhost:8080/candidates?text=I am the begt spell cherken"
# or
curl -d "I am the begt spell cherken" http://localhost:8080/candidates
    "results": [
            "candidates": [
            "len": 4,
            "pos_from": 9
            "candidates": [
            "len": 7,
            "pos_from": 20

Here pos_from - misspelled word first letter position, len - misspelled word len


To train custom model you need:

  1. Install cmake

  2. Clone and build jamspell:

git clone
cd JamSpell
mkdir build
cd build
cmake ..
  1. Prepare a utf-8 text file with sentences to train at (eg. sherlockholmes.txt) and another file with language alphabet (eg. alphabet_en.txt)

  2. Train model:

./main/jamspell train ../test_data/alphabet_en.txt ../test_data/sherlockholmes.txt model_sherlock.bin
  1. To evaluate spellchecker you can use evaluate/ script:
python evaluate/ -a alphabet_file.txt -jsp your_model.bin -mx 50000 your_test_data.txt
  1. You can use evaluate/ to generate you train/test data. It supports txt files, Leipzig Corpora Collection format and fb2 books.

Download models

Here is a few simple models. They trained on 300K news + 300k wikipedia sentences. We strongly recommend to train your own model, at least on a few million sentences to achieve better quality. See Train section above.