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AI-powered search engine

Project description

txtai: AI-powered search engine

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txtai builds an AI-powered index over sections of text. txtai supports building text indices to perform similarity searches and create extractive question-answering based systems.


NeuML uses txtai and/or the concepts behind it to power all of our Natural Language Processing (NLP) applications. Example applications:

  • paperai - AI-powered literature discovery and review engine for medical/scientific papers
  • tldrstory - AI-powered understanding of headlines and story text
  • neuspo - Fact-driven, real-time sports event and news site
  • codequestion - Ask coding questions directly from the terminal

txtai is built on the following stack:


The easiest way to install is via pip and PyPI

pip install txtai

You can also install txtai directly from GitHub. Using a Python Virtual Environment is recommended.

pip install git+

Python 3.6+ is supported


This project has dependencies that require compiling native code. Windows and macOS systems require the following additional steps. Most Linux environments will install without any additional steps.



  • Run the following before installing

    brew install libomp

    See this link for more information.


The examples directory has a series of examples and notebooks giving an overview of txtai. See the list of notebooks below.


Notebook Description
Introducing txtai Overview of the functionality provided by txtai Open In Colab
Extractive QA with txtai Extractive question-answering with txtai Open In Colab
Build an Embeddings index from a data source Embeddings index from a data source backed by word embeddings Open In Colab
Extractive QA with Elasticsearch Extractive question-answering with Elasticsearch Open In Colab


The following section goes over available settings for Embeddings and Extractor instances.


Embeddings methods are set through the constructor. Examples below.

# Transformers embeddings model
Embeddings({"method": "transformers",
            "path": "sentence-transformers/bert-base-nli-mean-tokens"})

# Word embeddings model
Embeddings({"path": vectors,
            "storevectors": True,
            "scoring": "bm25",
            "pca": 3,
            "quantize": True})


method: transformers|words

Sets the sentence embeddings method to use. When set to transformers, the embeddings object builds sentence embeddings using the sentence transformers. Otherwise a word embeddings model is used. Defaults to words.


path: string

Required field that sets the path for a vectors model. When method set to transformers, this must be a path to a Hugging Face transformers model. Otherwise, it must be a path to a local word embeddings model.


storevectors: boolean

Enables copying of a vectors model set in path into the embeddings models output directory on save. This option enables a fully encapsulated index with no external file dependencies.


scoring: bm25|tfidf|sif

For word embedding models, a scoring model allows building weighted averages of word vectors for a given sentence. Supports BM25, tf-idf and SIF (smooth inverse frequency) methods. If a scoring method is not provided, mean sentence embeddings are built.


pca: int

Removes n principal components from generated sentence embeddings. When enabled, a TruncatedSVD model is built to help with dimensionality reduction. After pooling of vectors creates a single sentence embedding, this method is applied.


backend: annoy|faiss|hnsw

Approximate Nearest Neighbor (ANN) index backend for storing generated sentence embeddings. Defaults to Faiss for Linux/macOS and Annoy for Windows. Faiss currently is not supported on Windows.


quantize: boolean

Enables quanitization of generated sentence embeddings. If the index backend supports it, sentence embeddings will be stored with 8-bit precision vs 32-bit. Only Faiss currently supports quantization.


Extractor methods are set as constructor arguments. Examples below.

Extractor(embeddings, path, quantize)


embeddings: Embeddings object instance

Embeddings object instance. Used to query and find candidate text snippets to run the question-answer model against.


path: string

Required path to a Hugging Face SQuAD fine-tuned model. Used to answer questions.


quantize: boolean

Enables dynamic quantization of the Hugging Face model. This is a runtime setting and doesn't save space. It is used to improve the inference time performance of the QA model.

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