Serverless Chat GPT API in Go

This blog shares how to create your own serverless ChatGPT API in Go.

What is Chat GPT ?

A natural language processing (NLP) model called GPT-3, also known as the "Generative Pre-training Transformer 3," was developed using text that humans produced. It can create its own human-like text using a range of languages and writing styles given some text input.

More details on Chat GPT and the excellent work can be found here.

What is Go?

Go, also referred to as Golang, is an open-source, statically typed, compiled computer language created by Google. It is designed to be straightforward, powerful, readable, and effective.


The following prerequisites are needed -

  • OpenAI Account - can be created here
  • SAM CLI Installed - can be found here
  • AWS Account(if you plan on deploying it to AWS)
Create Serverless API
  • Run sam init
  • Select AWS Quick Start Templates below
  • Edit the structure to create a folder called pkg and add a main.go
  • Create the functionality to call the Chat GPT API and return the response
  • Create a struct TextCompletionRequest like the below which matches the format, Chat GPT API accepts
type TextCompletionRequest struct {
	Model            string  `json:"model"`
	Prompt           string  `json:"prompt"`
	Temperature      float64 `json:"temperature"`
	MaxTokens        int     `json:"max_tokens"`
	TopP             float64 `json:"top_p"`
	FrequencyPenalty float64 `json:"frequency_penalty"`
	PresencePenalty  float64 `json:"presence_penalty"`
  • Create a struct TextCompletionResponse like the below which matches the format, Chat GPT API accepts
type Choice struct {
	Text         string      `json:"text"`
	Index        int         `json:"index"`
	Logprobs     interface{} `json:"logprobs"`
	FinishReason string      `json:"finish_reason"`

type TextCompletionResponse struct {
	ID      string   `json:"id"`
	Object  string   `json:"object"`
	Created int      `json:"created"`
	Model   string   `json:"model"`
	Choices []Choice `json:"choices"`
	Usage   struct {
		PromptTokens     int `json:"prompt_tokens"`
		CompletionTokens int `json:"completion_tokens"`
		TotalTokens      int `json:"total_tokens"`
	} `json:"usage"`
  • Create function ConverseWithGPT function below
func ConverseWithGPT(prompt string) (TextCompletionResponse, error) {
	httpReq := TextCompletionRequest{
		Model:            "text-davinci-003",
		Prompt:           prompt,
		Temperature:      0.7,
		MaxTokens:        100,
		TopP:             1.0,
		FrequencyPenalty: 0.0,
		PresencePenalty:  0.0,
	jsonValue, _ := json.Marshal(httpReq)

	bearer := "Bearer " + BearerToken

	req, _ := http.NewRequest("POST", ChatGPTHTTPAddress, bytes.NewBuffer(jsonValue))
	req.Header.Set("Authorization", bearer)
	req.Header.Add("Content-Type", "application/json")

	client := &http.Client{}
	resp, err := client.Do(req)
	if err != nil {
		return TextCompletionResponse{}, err
	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		return TextCompletionResponse{}, ErrNon200Response

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return TextCompletionResponse{}, err

	var textCompletionResponse TextCompletionResponse
	if err := json.Unmarshal(body, &textCompletionResponse); err != nil {
		fmt.Println("Can not unmarshal JSON")

	return textCompletionResponse, nil

To checkout, the code, check this repo.

Let's see it in action

Let's now run this locally.

Run the below command -

sam build
sam local start-api

Now, we can run this using postman

All right, Chat GPT suggested me some Netflix series to watch. Let me go watch them while you try running this yourself.

Cheers 🍻

Tirthankar Kundu

Tirthankar Kundu