Quickstart: Using C# to call the Text Analytics Cognitive Service

This article shows you how to detect language, analyze sentiment, and extract key phrases using the Text Analytics APIs with C#. The code was written to work on a .NET Core application, with minimal references to external libraries, so you could also run it on Linux or MacOS. The source code for this quickstart can be found on GitHub.

Refer to the API definitions for technical documentation for the APIs.


You must have a Cognitive Services API subscription with access to the Text Analytics API. If you don't have a subscription, you can create an account for free. Before continuing, you will need the Text Analytics subscription key provided after activating your account.

You must also have the endpoint and access key that was generated for you during sign-up.

Install the NuGet SDK Package

  1. Create a new Console solution using .netcoreapp2.0 and above in Visual Studio.
  2. Right click on the solution and click Manage NuGet Packages for Solution
  3. Select the Browse tab, and Search for Microsoft.Azure.CognitiveServices.Language.TextAnalytics


While you could call the HTTP endpoints directly from C#, the Microsoft.Azure.CognitiveServices.Language SDK makes it much easier to call the service without having to worry about serializing and deserializing JSON.

A few useful links:

Call the Text Analytics API using the SDK

  1. Replace Program.cs with the code provided below. This program demonstrates the capabilities of the Text Analytics API in three sections (language extraction, key-phrase extraction, and sentiment analysis).
  2. Replace the Ocp-Apim-Subscription-Key header value with an access key valid for your subscription.
  3. Replace the region in Endpoint. You can find your endpoint in the overview section of your Text Analytics resource in the Azure portal. Include only this portion of your endpoint: "https://[region].api.cognitive.microsoft.com".
  4. Run the program.
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

using Microsoft.Azure.CognitiveServices.Language.TextAnalytics;
using Microsoft.Azure.CognitiveServices.Language.TextAnalytics.Models;
using Microsoft.Rest;

namespace ConsoleApp1
    class Program
        private const string SubscriptionKey = ""; //Insert your Text Anaytics subscription key

        private class ApiKeyServiceClientCredentials : ServiceClientCredentials
            public override Task ProcessHttpRequestAsync(HttpRequestMessage request, CancellationToken cancellationToken)
                request.Headers.Add("Ocp-Apim-Subscription-Key", SubscriptionKey);
                return base.ProcessHttpRequestAsync(request, cancellationToken);

        static async Task Main(string[] args)

            // Create a client.
            ITextAnalyticsClient client = new TextAnalyticsClient(new ApiKeyServiceClientCredentials())
                Endpoint = "https://westus.api.cognitive.microsoft.com"
            }; //Replace 'westus' with the correct region for your Text Analytics subscription

            Console.OutputEncoding = System.Text.Encoding.UTF8;

            // Extracting language
            Console.WriteLine("===== LANGUAGE EXTRACTION ======");

            var langResults = await client.DetectLanguageAsync(
                new LanguageBatchInput(
                    new List<LanguageInput>
                          new LanguageInput(id: "1", text: "This is a document written in English."),
                          new LanguageInput(id: "2", text: "Este es un document escrito en Español."),
                          new LanguageInput(id: "3", text: "这是一个用中文写的文件")

            // Printing language results.
            foreach (var document in langResults.Documents)
                Console.WriteLine($"Document ID: {document.Id} , Language: {document.DetectedLanguages[0].Name}");

            // Getting key-phrases
            Console.WriteLine("\n\n===== KEY-PHRASE EXTRACTION ======");

            var kpResults = await client.KeyPhrasesAsync(
                new MultiLanguageBatchInput(
                    new List<MultiLanguageInput>
                        new MultiLanguageInput("ja", "1", "猫は幸せ"),
                        new MultiLanguageInput("de", "2", "Fahrt nach Stuttgart und dann zum Hotel zu Fu."),
                        new MultiLanguageInput("en", "3", "My cat is stiff as a rock."),
                        new MultiLanguageInput("es", "4", "A mi me encanta el fútbol!")

            // Printing keyphrases
            foreach (var document in kpResults.Documents)
                Console.WriteLine($"Document ID: {document.Id} ");

                Console.WriteLine("\t Key phrases:");

                foreach (string keyphrase in document.KeyPhrases)

            // Extracting sentiment
            Console.WriteLine("\n\n===== SENTIMENT ANALYSIS ======");

            var sentimentResults = await client.SentimentAsync(
                new MultiLanguageBatchInput(
                    new List<MultiLanguageInput>
                        new MultiLanguageInput("en", "1", "I had the best day of my life."),
                        new MultiLanguageInput("en", "2", "This was a waste of my time. The speaker put me to sleep."),
                        new MultiLanguageInput("es", "3", "No tengo dinero ni nada que dar..."),
                        new MultiLanguageInput("it", "4", "L'hotel veneziano era meraviglioso. È un bellissimo pezzo di architettura."),

            // Printing sentiment results
            foreach (var document in sentimentResults.Documents)
                Console.WriteLine($"Document ID: {document.Id} , Sentiment Score: {document.Score:0.00}");

            // Identify entities
            Console.WriteLine("\n\n===== ENTITIES ======");

            var entitiesResult = await client.EntitiesAsync(
                new MultiLanguageBatchInput(
                    new List<MultiLanguageInput>()
                        new MultiLanguageInput("en", "1", "Microsoft was founded by Bill Gates and Paul Allen on April 4, 1975, to develop and sell BASIC interpreters for the Altair 8800."),
                        new MultiLanguageInput("es", "2", "La sede principal de Microsoft se encuentra en la ciudad de Redmond, a 21 kilómetros de Seattle.")

            // Printing entities results
            foreach (var document in entitiesResult.Documents)
                Console.WriteLine($"Document ID: {document.Id} ");

                Console.WriteLine("\t Entities:");

                foreach (var entity in document.Entities)
                    Console.WriteLine($"\t\tName: {entity.Name},\tType: {entity.Type ?? "N/A"},\tSub-Type: {entity.SubType ?? "N/A"}");
                    foreach (var match in entity.Matches)
                        Console.WriteLine($"\t\t\tOffset: {match.Offset},\tLength: {match.Length},\tScore: {match.EntityTypeScore:F3}");


Application output

The application displays the following information:

Document ID: 1 , Language: English
Document ID: 2 , Language: Spanish
Document ID: 3 , Language: Chinese_Simplified

Document ID: 1
         Key phrases:
Document ID: 2
         Key phrases:
Document ID: 3
         Key phrases:
Document ID: 4
         Key phrases:

Document ID: 1 , Sentiment Score: 0.87
Document ID: 2 , Sentiment Score: 0.11
Document ID: 3 , Sentiment Score: 0.44
Document ID: 4 , Sentiment Score: 1.00

===== ENTITIES ======
Document ID: 1
                Name: Microsoft,        Type: Organization,     Sub-Type: N/A
                        Offset: 0,      Length: 9,      Score: 1.000
                Name: Bill Gates,       Type: Person,   Sub-Type: N/A
                        Offset: 25,     Length: 10,     Score: 1.000
                Name: Paul Allen,       Type: Person,   Sub-Type: N/A
                        Offset: 40,     Length: 10,     Score: 0.999
                Name: April 4,  Type: Other,    Sub-Type: N/A
                        Offset: 54,     Length: 7,      Score: 0.800
                Name: April 4, 1975,    Type: DateTime, Sub-Type: Date
                        Offset: 54,     Length: 13,     Score: 0.800
                Name: BASIC,    Type: Other,    Sub-Type: N/A
                        Offset: 89,     Length: 5,      Score: 0.800
                Name: Altair 8800,      Type: Other,    Sub-Type: N/A
                        Offset: 116,    Length: 11,     Score: 0.800
Document ID: 2
                Name: Microsoft,        Type: Organization,     Sub-Type: N/A
                        Offset: 21,     Length: 9,      Score: 1.000
                Name: Redmond (Washington),     Type: Location, Sub-Type: N/A
                        Offset: 60,     Length: 7,      Score: 0.991
                Name: 21 kilómetros,    Type: Quantity, Sub-Type: Dimension
                        Offset: 71,     Length: 13,     Score: 0.800
                Name: Seattle,  Type: Location, Sub-Type: N/A
                        Offset: 88,     Length: 7,      Score: 1.000

Next steps

See also

Text Analytics overview Frequently asked questions (FAQ)