What is Language Understanding (LUIS)?


TLS 1.2 is now enforced for all HTTP requests to this service. For more information, see Azure Cognitive Services security.

Language Understanding (LUIS) is a cloud-based API service that applies custom machine-learning intelligence to a user's conversational, natural language text to predict overall meaning, and pull out relevant, detailed information.

A client application for LUIS is any conversational application that communicates with a user in natural language to complete a task. Examples of client applications include social media apps, chat bots, and speech-enabled desktop applications.

Conceptual image of 3 client applications working with Cognitive Services Language Understanding (LUIS)

Use LUIS in a chat bot

Once the LUIS app is published, a client application sends utterances (text) to the LUIS natural language processing endpoint API and receives the results as JSON responses. A common client application for LUIS is a chat bot.

Conceptual imagery of LUIS working with Chat bot to predict user text with natural language understanding (NLP)

Step Action
1 The client application sends the user utterance (text in their own words), "I want to call my HR rep." to the LUIS endpoint as an HTTP request.
2 LUIS enables you to craft your custom language models to add intelligence to your application. Machine learned language models take the user's unstructured input text and returns a JSON-formatted response, with a top intent, HRContact. The minimum JSON endpoint response contains the query utterance, and the top scoring intent. It can also extract data such as the Contact Type entity.
3 The client application uses the JSON response to make decisions about how to fulfill the user's requests. These decisions can include decision tree in the bot framework code and calls to other services.

The LUIS app provides intelligence so the client application can make smart choices. LUIS doesn't provide those choices.

Natural language processing

Your LUIS app contains a domain-specific natural language model. You can start the LUIS app with a prebuilt domain model, build your own model, or blend pieces of a prebuilt domain with your own custom information.

  • Prebuilt model LUIS has many prebuilt domain models including intents, utterances, and prebuilt entities. You can use the prebuilt entities without having to use the intents and utterances of the prebuilt model. Prebuilt domain models include the entire design for you and are a great way to start using LUIS quickly.

  • Custom model LUIS gives you several ways to identify your own custom models including intents, and entities. Entities include machine-learning entities, specific or literal entities, and a combination of machine-learning and literal.

Build the LUIS model

Build the model with the authoring APIs or with the LUIS portal.

The LUIS model begins with categories of user intentions called intents. Each intent needs examples of user utterances. Each utterance can provide data that needs to be extracted.

Example user utterance Intent Extracted data
Book a flight to Seattle? BookFlight Seattle
When does your store open? StoreHoursAndLocation open
Schedule a meeting at 1pm with Bob in Distribution ScheduleMeeting 1pm, Bob

Query prediction endpoint

After your app is trained and published to the endpoint, the client application sends utterances to the prediction endpoint API. The API applies the app to the utterance for analysis and responds with the prediction results in a JSON format.

The minimum JSON endpoint response contains the query utterance, and the top scoring intent. It can also extract data such as the following Contact Type entity and overall sentiment.

    "query": "I want to call my HR rep",
    "prediction": {
        "normalizedQuery": "i want to call my hr rep",
        "topIntent": "HRContact",
        "intents": {
            "HRContact": {
                "score": 0.8582669
        "entities": {
            "Contact Type": [
        "sentiment": {
            "label": "negative",
            "score": 0.103343368

Improve model prediction

After your LUIS app is published and receives real user utterances, LUIS provides active learning of endpoint utterances to improve prediction accuracy.

Development lifecycle

LUIS provides tools, versioning, and collaboration with other LUIS authors to integrate into the full development life cycle.

Implementing LUIS

Language Understanding (LUIS), as a REST API, can be used with any product, service, or framework with an HTTP request. The following list contains the top Microsoft products and services used with LUIS.

The top client application for LUIS is:

  • Web app bot quickly creates a LUIS-enabled chat bot to talk with a user via text input. Uses Bot Framework version 4.x for a complete bot experience.

Tools to quickly and easily use LUIS with a bot:

  • LUIS CLI The NPM package provides authoring and prediction with as either a stand-alone command-line tool or as import.
  • LUISGen LUISGen is a tool for generating strongly typed C# and typescript source code from an exported LUIS model.
  • Dispatch allows several LUIS and QnA Maker apps to be used from a parent app using dispatcher model.
  • LUDown LUDown is a command-line tool that helps manage language models for your bot.
  • Bot framework - Composer - an integrated development tool for developers and multi-disciplinary teams to build bots and conversational experiences with the Microsoft Bot Framework

Other Cognitive Services used with LUIS:

  • QnA Maker allows several types of text to combine into a question and answer knowledge base.
  • Speech service converts spoken language requests into text.
  • Conversation learner allows you to build bot conversations quicker with LUIS.

Samples using LUIS:

Next steps