diff --git a/blockchain.js b/blockchain.js
new file mode 100644
index 0000000..e6c0d4a
--- /dev/null
+++ b/blockchain.js
@@ -0,0 +1,62 @@
+const crypto = require("crypto");
+
+// 🔗 Klasa pojedynczego bloku
+class Block {
+  constructor(index, timestamp, data, previousHash = "") {
+    this.index = index;
+    this.timestamp = timestamp;
+    this.data = data;
+    this.previousHash = previousHash;
+    this.hash = this.calculateHash();
+  }
+
+  calculateHash() {
+    return crypto
+      .createHash("sha256")
+      .update(
+        this.index +
+          this.previousHash +
+          this.timestamp +
+          JSON.stringify(this.data)
+      )
+      .digest("hex");
+  }
+}
+
+// 🧠 Klasa prostego łańcucha bloków
+class Blockchain {
+  constructor() {
+    this.chain = [this.createGenesisBlock()];
+  }
+
+  createGenesisBlock() {
+    return new Block(0, Date.now().toString(), "Genesis Block", "0");
+  }
+
+  getLatestBlock() {
+    return this.chain[this.chain.length - 1];
+  }
+
+  addBlock(newBlock) {
+    newBlock.previousHash = this.getLatestBlock().hash;
+    newBlock.hash = newBlock.calculateHash();
+    this.chain.push(newBlock);
+  }
+
+  isChainValid() {
+    for (let i = 1; i < this.chain.length; i++) {
+      const current = this.chain[i];
+      const previous = this.chain[i - 1];
+
+      if (current.hash !== current.calculateHash()) return false;
+      if (current.previousHash !== previous.hash) return false;
+    }
+    return true;
+  }
+}
+
+// 📦 Eksport
+module.exports = {
+  Block,
+  Blockchain,
+};