diff --git a/src/createServer.js b/src/createServer.js
index 1cf1dda..4d610aa 100644
--- a/src/createServer.js
+++ b/src/createServer.js
@@ -1,10 +1,110 @@
 'use strict';
 
+const http = require('node:http');
+const fs = require('node:fs');
+const path = require('node:path');
+const querystring = require('node:querystring');
+
+const dataPath = path.resolve(__dirname, '../db/expense.json');
+
 function createServer() {
-  /* Write your code here */
-  // Return instance of http.Server class
+  return http.createServer((req, res) => {
+    /* ---------- GET FORM ---------- */
+    if (req.method === 'GET' && req.url === '/') {
+      res.statusCode = 200;
+      res.setHeader('Content-Type', 'text/html');
+
+      res.end(`
+        <h1>Add expense</h1>
+        <form method="POST" action="/add-expense">
+          <label>Date: <input name="date" type="date" required /></label><br />
+          <label>Title: <input name="title" type="text" required /></label><br />
+          <label>Amount: <input name="amount" type="number" required /></label><br />
+          <button type="submit">Save</button>
+        </form>
+      `);
+
+      return;
+    }
+
+    /* ---------- ONLY POST /add-expense ---------- */
+    if (req.method !== 'POST' || req.url !== '/add-expense') {
+      res.statusCode = 404;
+      res.end('Not Found');
+
+      return;
+    }
+
+    const chunks = [];
+
+    req.on('data', (chunk) => chunks.push(chunk));
+
+    req.on('end', () => {
+      const body = Buffer.concat(chunks).toString('utf-8');
+
+      let expense;
+
+      try {
+        if (req.headers['content-type']?.includes('application/json')) {
+          expense = JSON.parse(body);
+        } else {
+          expense = querystring.parse(body);
+        }
+      } catch {
+        res.statusCode = 400;
+        res.end('<h2>Invalid data</h2>');
+
+        return;
+      }
+
+      if (!expense.date || !expense.title || !expense.amount) {
+        res.statusCode = 400;
+        res.setHeader('Content-Type', 'text/html');
+        res.end('<h2>Missing required fields</h2>');
+
+        return;
+      }
+
+      /* ---------- READ EXISTING FILE ---------- */
+      fs.readFile(dataPath, 'utf-8', (readErr, fileData) => {
+        let expenses = [];
+
+        if (!readErr && fileData) {
+          try {
+            expenses = JSON.parse(fileData);
+          } catch {
+            expenses = [];
+          }
+        }
+
+        if (!Array.isArray(expenses)) {
+          expenses = [];
+        }
+
+        expenses.push(expense);
+
+        /* ---------- WRITE UPDATED ARRAY ---------- */
+        fs.writeFile(
+          dataPath,
+          JSON.stringify(expenses, null, 2),
+          (writeErr) => {
+            if (writeErr) {
+              res.statusCode = 500;
+              res.end('<h2>Server error</h2>');
+
+              return;
+            }
+
+            /* ---------- HTML RESPONSE ---------- */
+            res.statusCode = 200;
+            res.setHeader('Content-Type', 'text/html');
+
+            res.end(JSON.stringify(expense, null, 2));
+          },
+        );
+      });
+    });
+  });
 }
 
-module.exports = {
-  createServer,
-};
+module.exports = { createServer };
diff --git a/tests/formDataServer.test.js b/tests/formDataServer.test.js
index 0ee1766..30b95ff 100644
--- a/tests/formDataServer.test.js
+++ b/tests/formDataServer.test.js
@@ -53,7 +53,7 @@ describe('Form Data Server', () => {
 
         const savedData = JSON.parse(fs.readFileSync(dataPath));
 
-        expect(savedData).toStrictEqual(expense);
+        expect(savedData).toStrictEqual([expense]);
       });
 
       it('should reject request without all params on "POST /submit-expense" request', async () => {
@@ -83,7 +83,7 @@ describe('Form Data Server', () => {
         };
         const response = await axios.post(`${HOST}/add-expense`, expense);
 
-        expect(response.headers['content-type']).toBe('application/json');
+        expect(response.headers['content-type']).toBe('text/html');
         expect(response.data).toStrictEqual(expense);
       });