LLM APIs - lesson 1 | HackIndia Skills

LLM APIs - lesson 1 | HackIndia Skills | HackIndia

Your to-do

Set up safely

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.

Install the official OpenAI SDK in your server project.
Create a .env file for local development.
Store your key as OPENAI_API_KEY, not inside code.
Add .env to .gitignore before pushing to GitHub.
Call OpenAI only from a backend route or server function.

0 of 5 done

npm install openai

Example

Minimal server route

This example uses Express because it is easy to read. The same idea works in Next.js, Hono, Fastify, Django, or Flask: keep the key on the server and expose your own route to the UI.

The route accepts user text, sends product rules in instructions, and returns one answer.

import express from "express";
import OpenAI from "openai";

const app = express();
app.use(express.json());

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

app.post("/api/ai", async (req, res) => {
  try {
    const userText = req.body.message;

    if (!userText || typeof userText !== "string") {
      return res.status(400).json({ error: "message is required" });
    }

    const response = await client.responses.create({
      model: "gpt-4o-mini",
      instructions: "You are a helpful assistant. Give a clear answer in under 120 words.",
      input: userText,
      max_output_tokens: 200
    });

    res.json({ answer: response.output_text });
  } catch (error) {
    console.error(error);
    res.status(500).json({ error: "AI request failed" });
  }
});

app.listen(3000, () => {
  console.log("Server running on http://localhost:3000");
});

Example

Local files

Your .env is private. Your .env.example is safe to commit because it shows the name of the variable without the real value.

This matters for hackathon judging. A reviewer should be able to set up your repo without seeing your secret key.

.env
OPENAI_API_KEY=sk-your-real-key-here

.env.example
OPENAI_API_KEY=replace_with_your_key

.gitignore
.env
node_modules

Call a model safely

One rule

What goes where

Set up safely

Minimal server route

Local files

Common leak

Check AI code

Do this now

Quick check