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Evaluation code for various unsupervised automated metrics for NLG (Natural Language Generation). It takes as input a hypothesis file, and one or more references files and outputs values of metrics. Rows across these files should correspond to the same example.


  • BLEU
  • CIDEr
  • SkipThought cosine similarity
  • Embedding Average cosine similarity
  • Vector Extrema cosine similarity
  • Greedy Matching score


Install Java 1.8.0 (or higher).

Install the Python dependencies, run:

pip install git+[email protected]

If you are using macOS High Sierra or higher, then run this to allow multithreading:


Simple setup (download required data (e.g. models, embeddings) and external code files), run:

nlg-eval --setup

If you're setting this up from the source code or you're on Windows and not using a Bash terminal, then you might get errors about nlg-eval not being found. You will need to find the nlg-eval script. See here for details.

Custom Setup

# If you don't like the default path (~/.cache/nlgeval) for the downloaded data,
# then specify a path where you want the files to be downloaded.
# The value for the data path is stored in ~/.config/nlgeval/rc.json and can be overwritten by
# setting the NLGEVAL_DATA environment variable.
nlg-eval --setup ${data_path}

Validate the Setup (Optional)

(These examples were made with Git Bash on Windows)

All of the data files should have been downloaded, you should see sizes like:

$ ls -l ~/.cache/nlgeval/
total 6003048
-rw-r--r-- 1 ...  289340074 Sep 12  2018 bi_skip.npz
-rw-r--r-- 1 ...        689 Sep 12  2018 bi_skip.npz.pkl
-rw-r--r-- 1 ... 2342138474 Sep 12  2018 btable.npy
-rw-r--r-- 1 ...    7996547 Sep 12  2018 dictionary.txt
-rw-r--r-- 1 ...   21494787 Jan 22  2019 glove.6B.300d.model.bin
-rw-r--r-- 1 ...  480000128 Jan 22  2019 glove.6B.300d.model.bin.vectors.npy
-rw-r--r-- 1 ...  663989216 Sep 12  2018 uni_skip.npz
-rw-r--r-- 1 ...        693 Sep 12  2018 uni_skip.npz.pkl
-rw-r--r-- 1 ... 2342138474 Sep 12  2018 utable.npy

You can also verify some checksums:

$ cd ~/.cache/nlgeval/
$ md5sum *
9a15429d694a0e035f9ee1efcb1406f3 *bi_skip.npz
c9b86840e1dedb05837735d8bf94cee2 *bi_skip.npz.pkl
022b5b15f53a84c785e3153a2c383df6 *btable.npy
26d8a3e6458500013723b380a4b4b55e *dictionary.txt
f561ab0b379e23cbf827a054f0e7c28e *glove.6B.300d.model.bin
be5553e91156471fe35a46f7dcdfc44e *glove.6B.300d.model.bin.vectors.npy
8eb7c6948001740c3111d71a2fa446c1 *uni_skip.npz
e1a0ead377877ff3ea5388bb11cfe8d7 *uni_skip.npz.pkl
5871cc62fc01b79788c79c219b175617 *utable.npy
$ sha256sum *
8ab7965d2db5d146a907956d103badfa723b57e0acffb75e10198ba9f124edb0 *bi_skip.npz
d7e81430fcdcbc60b36b92b3f879200919c75d3015505ee76ae3b206634a0eb6 *bi_skip.npz.pkl
4a4ed9d7560bb87f91f241739a8f80d8f2ba787a871da96e1119e913ccd61c53 *btable.npy
4dc5622978a30cddea8c975c871ea8b6382423efb107d27248ed7b6cfa490c7c *dictionary.txt
10c731626e1874effc4b1a08d156482aa602f7f2ca971ae2a2f2cd5d70998397 *glove.6B.300d.model.bin
20dfb1f44719e2d934bfee5d39a6ffb4f248bae2a00a0d59f953ab7d0a39c879 *glove.6B.300d.model.bin.vectors.npy
7f40ff16ff5c54ce9b02bd1a3eb24db3e6adaf7712a7a714f160af3a158899c8 *uni_skip.npz
d58740d46cba28417cbc026af577f530c603d81ac9de43ffd098f207c7dc4411 *uni_skip.npz.pkl
790951d4b08e843e3bca0563570f4134ffd17b6bd4ab8d237d2e5ae15e4febb3 *utable.npy

If you're ensure that the setup was successful, you can run the tests:

pip install pytest

It might take a few minutes and you might see warnings but they should pass.


Once setup has completed, the metrics can be evaluated with a Python API or in the command line.

Examples of the Python API can be found in


nlg-eval --hypothesis=examples/hyp.txt --references=examples/ref1.txt --references=examples/ref2.txt

where each line in the hypothesis file is a generated sentence and the corresponding lines across the reference files are ground truth reference sentences for the corresponding hypothesis.

functional API: for the entire corpus

from nlgeval import compute_metrics
metrics_dict = compute_metrics(hypothesis='examples/hyp.txt',
                               references=['examples/ref1.txt', 'examples/ref2.txt'])

functional API: for only one sentence

from nlgeval import compute_individual_metrics
metrics_dict = compute_individual_metrics(references, hypothesis)

where references is a list of ground truth reference text strings and hypothesis is the hypothesis text string.

object oriented API for repeated calls in a script - single example

from nlgeval import NLGEval
nlgeval = NLGEval()  # loads the models
metrics_dict = nlgeval.compute_individual_metrics(references, hypothesis)

where references is a list of ground truth reference text strings and hypothesis is the hypothesis text string.

object oriented API for repeated calls in a script - multiple examples

from nlgeval import NLGEval
nlgeval = NLGEval()  # loads the models
metrics_dict = nlgeval.compute_metrics(references, hypothesis)

where references is a list of lists of ground truth reference text strings and hypothesis is a list of hypothesis text strings. Each inner list in references is one set of references for the hypothesis (a list of single reference strings for each sentence in hypothesis in the same order).


If you use this code as part of any published research, please cite the following paper:

Shikhar Sharma, Layla El Asri, Hannes Schulz, and Jeremie Zumer. "Relevance of Unsupervised Metrics in Task-Oriented Dialogue for Evaluating Natural Language Generation" arXiv preprint arXiv:1706.09799 (2017)

    author  = {Sharma, Shikhar and El Asri, Layla and Schulz, Hannes and Zumer, Jeremie},
    title   = {Relevance of Unsupervised Metrics in Task-Oriented Dialogue for Evaluating Natural Language Generation},
    journal = {CoRR},
    volume  = {abs/1706.09799},
    year    = {2017},
    url     = {}



nlg-eval --hypothesis=examples/hyp.txt --references=examples/ref1.txt --references=examples/ref2.txt


Bleu_1: 0.550000
Bleu_2: 0.428174
Bleu_3: 0.284043
Bleu_4: 0.201143
METEOR: 0.295797
ROUGE_L: 0.522104
CIDEr: 1.242192
SkipThoughtsCosineSimilarity: 0.626149
EmbeddingAverageCosineSimilarity: 0.884690
VectorExtremaCosineSimilarity: 0.568696
GreedyMatchingScore: 0.784205


If you have issues with Meteor then you can try lowering the mem variable in

Important Note

CIDEr by default (with idf parameter set to "corpus" mode) computes IDF values using the reference sentences provided. Thus, CIDEr score for a reference dataset with only 1 image (or example for NLG) will be zero. When evaluating using one (or few) images, set idf to "coco-val-df" instead, which uses IDF from the MSCOCO Vaildation Dataset for reliable results. This has not been adapted in this code. For this use-case, apply patches from vrama91/coco-caption.

External data directory

To mount an already prepared data directory to a Docker container or share it between users, you can set the NLGEVAL_DATA environment variable to let nlg-eval know where to find its models and data. E.g.


This variable overrides the value provided during setup (stored in ~/.config/nlgeval/rc.json)

Microsoft Open Source Code of Conduct

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact [email protected] with any additional questions or comments.



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