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Integrating a .NET 8 web API with OpenAI ChatGPT

✏️ Lucas dos Santos Alves   ⌚ 4 min read

AI is now part of a developer day. 🤖
Knowing how to use these available AI tools as productivity boosters has become very relevant.

This post shows how you can create a .NET 8 web API and integrate it with OpenAI ChatGPT API to get a response based on a text.

Prerequisites

  • .NET 8 SDK
  • OpenAI Account & API key

Create an OpenAI API key

  • Go to OpenAI Platform and log in

  • Go to 'API keys'

  • Select 'Create new secret key'

Create a .NET 8 Web Api project

dotnet add package OpenAI
  • Add your OpenAI API key to appsettings.json
{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*",
  "OpenAIChatGpt": {
    "Key": "YOUR-API-KEY-HERE"
  }
}

  • Create a folder called Settings

  • Create a static class called OpenAIChatGptSettings inside of it

  • Create a method to obtain the OpenAI key from appsettings.json

    public static class OpenAIChatGptSettings
    {
        public static WebApplicationBuilder AddOpenAIChatGPT(this WebApplicationBuilder builder, IConfiguration configuration)
        {
            var chatGptKey = configuration["OpenAIChatGpt:Key"];

            var chat = new OpenAIAPI(chatGptKey);

            builder.Services.AddSingleton(chat);

            return builder;
        }
    }
  • Add this settings to Program.cs
builder.AddOpenAIChatGPT(builder.Configuration);

  • Create a new controller called ChatGptController

  • Create a GET method to consult Chat GPT based on text

using Microsoft.AspNetCore.Mvc;
using OpenAI_API;
using OpenAI_API.Completions;
using OpenAI_API.Models;
using Swashbuckle.AspNetCore.Annotations;

namespace dotnet_gpt.api.Controllers
{
    [Route("api/chat-gpt")]
    [ApiController]
    public class ChatGptController : ControllerBase
    {
        private readonly OpenAIAPI _chatGpt;

        public ChatGptController(OpenAIAPI chatGpt)
        {
            _chatGpt = chatGpt;
        }

        [HttpGet]
        [SwaggerOperation("Interact with OpenAI ChatGPT through text")]
        public async Task<IActionResult> GetResponseFromChatGpt(string text)
        {
            ArgumentException.ThrowIfNullOrWhiteSpace(text);

            var response = string.Empty;

            var completionRequest = new CompletionRequest
            {
                Prompt = text,
                Model = Model.DefaultModel,
                MaxTokens = 200,
            };

            var result = await _chatGpt.Completions.CreateCompletionAsync(completionRequest);

            if (result.Completions.Any())
                response = result.Completions.First().Text;

            return Ok(response);
        }
    }
}

On the completions, which are the chat conversations, we're just getting the first text response.

.NET 8 swagger result
.NET 8 swagger result

We used the default model to get the response, but more models can be explored. Some of them are exclusive for paid plans.

  • More about OpenAI models

GitHub repo for this project

Troubleshooting

If you got the following error return 'OpenAI API error 429: "You exceeded your current quota, please check your plan and billing details"' you can troubleshoot:

  • If your OpenAI API key was created recently, try to wait a little bit, at least 10 min
  • Add a credit or debit card in payment methods in your OpenAI account (if you do, do not forget to set limits to not incur charges)
  • Generate a new API key and add it to the project again
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