How to Create a Database in Firebase 🔥 — Complete Guide 2026

// WARNING: expires in 30 days!
{
  "rules": {
    ".read":  "now < 1748649600000",
    ".write": "now < 1748649600000"
  }
}

{
  "rules": {
    "scores": {
      ".read":  true,
      ".write": true,
      "$id": {
        ".validate": "newData.hasChildren(['name','score','timestamp'])",
        "name":  { ".validate": "newData.isString() && newData.val().length <= 50" },
        "score": { ".validate": "newData.isNumber() && newData.val() >= 0" }
      }
    }
  }
}

const firebaseConfig = {
  apiKey:            "AIzaSy-YOUR-KEY",
  authDomain:        "your-project.firebaseapp.com",
  databaseURL:       "https://your-project-rtdb.firebasedatabase.app",
  projectId:         "your-project-id",
  storageBucket:     "your-project.appspot.com",
  messagingSenderId: "123456789",
  appId:             "1:123:web:abc"
};

const DB_URL = "https://your-project-rtdb.firebasedatabase.app";

async function saveScore(name, score) {
  const res = await fetch(DB_URL + "/scores.json", {
    method:  "POST",
    headers: { "Content-Type": "application/json" },
    body:    JSON.stringify({
      name, score,
      timestamp: new Date().toISOString()
    })
  });
  const result = await res.json();
  console.log("Saved! ID:", result.name);
}

saveScore("Rahul", 95);

async function loadScores() {
  const res  = await fetch(DB_URL + "/scores.json");
  const data = await res.json();

  if (!data) { console.log("No data"); return; }

  const scores = Object.values(data);
  scores.sort((a, b) => b.score - a.score);
  scores.forEach(e => console.log(e.name, e.score));
}

loadScores();

// Update specific fields only
async function updateScore(id, newScore) {
  await fetch(DB_URL + `/scores/${id}.json`, {
    method:  "PATCH",
    headers: { "Content-Type": "application/json" },
    body:    JSON.stringify({ score: newScore })
  });
}

// Delete one entry
async function deleteEntry(id) {
  await fetch(DB_URL + `/scores/${id}.json`, {
    method: "DELETE"
  });
}

<!-- Firebase App (always first) -->
<script src="https://www.gstatic.com/firebasejs/10.8.0/firebase-app-compat.js"></script>

<!-- Realtime Database -->
<script src="https://www.gstatic.com/firebasejs/10.8.0/firebase-database-compat.js"></script>

firebase.initializeApp(firebaseConfig);
const db = firebase.database();

// Write
db.ref("scores").push({ name: "Rahul", score: 95 });

// Read once
db.ref("scores").once("value", snap => console.log(snap.val()));

// Real-time listener (auto-updates!)
db.ref("scores").on("value", snap => render(snap.val()));

// Update partial fields
db.ref(`scores/${entryId}`).update({ score: 100 });

// Delete
db.ref(`scores/${entryId}`).remove();

// Stop listener
db.ref("scores").off();

// Top 10 scores (SDK)
db.ref("scores")
  .orderByChild("score")
  .limitToLast(10)
  .once("value", snap => {
    const arr = [];
    snap.forEach(c => arr.push(c.val()));
    console.log(arr.reverse());
  });

// REST API query params
const url = DB_URL + '/scores.json?orderBy="score"&limitToLast=10';
const data = await (await fetch(url)).json();

{
  "rules": {

    // Only logged-in users
    "posts": {
      ".read":  "auth != null",
      ".write": "auth != null"
    },

    // Users can only read/write THEIR OWN data
    "users": {
      "$uid": {
        ".read":  "auth.uid == $uid",
        ".write": "auth.uid == $uid"
      }
    }
  }
}

const db = firebase.firestore();

// Add document (auto ID)
db.collection("scores").add({ name: "Rahul", score: 95 });

// Advanced query
db.collection("scores")
  .where("score", ">=", 50)
  .orderBy("score", "desc")
  .limit(10)
  .get().then(snap =>
    snap.forEach(d => console.log(d.data()))
  );

// Real-time
db.collection("scores").onSnapshot(snap =>
  snap.forEach(d => console.log(d.data()))
);

<input  id="name"    placeholder="Your Name"/>
<input  id="email"   placeholder="Email"/>
<textarea id="msg"  placeholder="Message..." rows="4"></textarea>
<button onclick="send()">Send</button>
<div id="status"></div>

<script>
const DB = "https://YOUR-PROJECT-rtdb.firebasedatabase.app";

async function send() {
  const name    = document.getElementById("name").value.trim();
  const email   = document.getElementById("email").value.trim();
  const message = document.getElementById("msg").value.trim();
  const status  = document.getElementById("status");

  if (!name || !email || !message) {
    status.style.color  = "red";
    status.textContent  = "Please fill all fields!";
    return;
  }
  try {
    await fetch(DB + "/contacts.json", {
      method:  "POST",
      headers: { "Content-Type": "application/json" },
      body:    JSON.stringify({ name, email, message,
        timestamp: new Date().toISOString() })
    });
    status.style.color  = "green";
    status.textContent  = "Message sent!";
  } catch (err) {
    status.style.color  = "red";
    status.textContent  = "Error! Try again.";
  }
}
</script>