LLM APIs - lesson 6 | HackIndia Skills

Key point

One habit

Every AI feature should record tokens per request. If you cannot see usage, you cannot explain cost when your demo gets shared in a college WhatsApp group.

Tokens are what the model processes. Input, cached input, and output tokens can have different prices, based on the model.

What tokens mean

A token can be a character, part of a word, a whole word, punctuation, or spaces. For English, OpenAI gives a rough estimate: 1 token is about 4 characters, and 100 tokens are about 75 words.

Reasoning tokens may not appear in the visible answer. They still count toward output usage and are billed as output tokens.

Common mistake

Old token names

Many older tutorials use max_tokens as a general setting. Do not copy that blindly.

With the Responses API, use max_output_tokens. Chat Completions uses max_completion_tokens, but this track uses Responses because OpenAI recommends it for text generation apps.

Example

Log usage

Add one small log line after your server route gets a response. Keep this on the backend, along with your API key.

Field names can vary by SDK response shape, so log the full usage object first. Then store only the numbers your app needs.

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.OPENAI_API_KEY,
});

export async function POST(req) {
  const { question } = await req.json();

  const response = await client.responses.create({
    model: "gpt-4o-mini",
    instructions: "Answer like a helpful project mentor. Keep it short.",
    input: question,
    max_output_tokens: 300,
  });

  console.log("openai_usage", {
    response_id: response.id,
    usage: response.usage,
  });

  return Response.json({
    answer: response.output_text,
    usage: response.usage,
  });
}

Your to-do

Add a budget guard

Do each one yourself, then tap it to tick it off. The ticks are only a checklist for you: they are not marked or scored.

Set max_output_tokens for every request that generates text.
Log response id, route name, model, and usage for each request.
Keep a simple daily count in your database or server logs.
Return a friendly message if a user keeps retrying the same expensive action.
Review the OpenAI Usage Dashboard after testing, because Playground usage also counts.

0 of 5 done

Tip

Estimate before building

Before coding a feature, write one sample input and one expected answer. Estimate tokens roughly using 100 tokens as about 75 English words.

Then check real usage from the API response. Use pricing from the OpenAI pricing page for your chosen model, because prices depend on model and token category.