Node.js/TypeScript: ChatGPT API (gpt-3.5-turbo) messages token calculator

chatgpt-api-gpt-3.5-turbo-messages-token-calculator.ts

// Author: mnemotiv
// Donate: https://donate.stripe.com/9AQbJM4xC62P0xieUU

// Don't forget to run this first:
// npm i @dqbd/tiktoken

import { get_encoding } from '@dqbd/tiktoken';
import type { ChatCompletionRequestMessage } from 'openai';

const countTokens = (messages: ChatCompletionRequestMessage[]): number => {
  const tokenizer = get_encoding('cl100k_base');

  return messages
    .map(
      (message) => Object.entries(message)
        .map(
          ([key, value]) => tokenizer.encode(value).length - (key === 'name' ? 1 : 0),
        )
        .reduce((a, b) => a + b, 4),
    )
    .reduce((a, b) => a + b, 2);
};