diff --git a/src/CurrencyConverter.php b/src/CurrencyConverter.php
new file mode 100644
index 00000000..0d77b44b
--- /dev/null
+++ b/src/CurrencyConverter.php
@@ -0,0 +1,107 @@
+<?php
+/**
+ * Currency Converter.
+ *
+ * PHP version 7.4
+ *
+ * @category Challenge
+ * @package  Back-end
+ * @author   Seu Nome <seu-email@seu-provedor.com>
+ * @license  http://opensource.org/licenses/MIT MIT
+ * @link     https://github.com/apiki/back-end-challenge
+ */
+
+declare(strict_types=1);
+
+namespace App;
+
+/**
+ * Class CurrencyConverter
+ *
+ * @category Challenge
+ * @package  Back-end
+ * @author   Seu Nome <seu-email@seu-provedor.com>
+ * @license  http://opensource.org/licenses/MIT MIT
+ * @link     https://github.com/apiki/back-end-challenge
+ */
+class CurrencyConverter
+{
+    private const CURRENCY_SYMBOLS = [
+        'USD' => '$',
+        'BRL' => 'R$',
+        'EUR' => '€',
+    ];
+
+    private const VALID_CONVERSIONS = [
+        'BRL' => ['USD', 'EUR'],
+        'USD' => ['BRL'],
+        'EUR' => ['BRL'],
+    ];
+
+    /**
+     * Convert currency.
+     *
+     * @param float  $amount The amount to convert.
+     * @param string $from   The source currency.
+     * @param string $to     The target currency.
+     * @param float  $rate   The exchange rate.
+     *
+     * @return array
+     */
+    public function convert(
+        float $amount,
+        string $from,
+        string $to,
+        float $rate
+    ): array {
+        $this->_validate($amount, $from, $to, $rate);
+
+        $convertedValue = $amount * $rate;
+
+        return [
+            'valorConvertido' => $convertedValue,
+            'simboloMoeda'    => self::CURRENCY_SYMBOLS[$to],
+        ];
+    }
+
+    /**
+     * Validate conversion parameters.
+     *
+     * @param float  $amount The amount to convert.
+     * @param string $from   The source currency.
+     * @param string $to     The target currency.
+     * @param float  $rate   The exchange rate.
+     *
+     * @return void
+     *
+     * @throws \InvalidArgumentException When parameters are invalid.
+     */
+    private function _validate(
+        float $amount,
+        string $from,
+        string $to,
+        float $rate
+    ): void {
+        if ($amount <= 0) {
+            throw new \InvalidArgumentException('Invalid amount.');
+        }
+
+        if ($rate <= 0) {
+            throw new \InvalidArgumentException('Invalid rate.');
+        }
+
+        if (!isset(self::CURRENCY_SYMBOLS[$from])) {
+            throw new \InvalidArgumentException('Invalid source currency.');
+        }
+
+        if (!isset(self::CURRENCY_SYMBOLS[$to])) {
+            throw new \InvalidArgumentException('Invalid target currency.');
+        }
+
+        if (!isset(self::VALID_CONVERSIONS[$from])
+            || !in_array($to, self::VALID_CONVERSIONS[$from])
+        ) {
+            throw new \InvalidArgumentException('Invalid conversion.');
+        }
+    }
+}
diff --git a/src/Router.php b/src/Router.php
new file mode 100644
index 00000000..b5745ead
--- /dev/null
+++ b/src/Router.php
@@ -0,0 +1,90 @@
+<?php
+/**
+ * Router.
+ *
+ * PHP version 7.4
+ *
+ * @category Challenge
+ * @package  Back-end
+ * @author   Seu Nome <seu-email@seu-provedor.com>
+ * @license  http://opensource.org/licenses/MIT MIT
+ * @link     https://github.com/apiki/back-end-challenge
+ */
+
+declare(strict_types=1);
+
+namespace App;
+
+/**
+ * Class Router
+ *
+ * @category Challenge
+ * @package  Back-end
+ * @author   Seu Nome <seu-email@seu-provedor.com>
+ * @license  http://opensource.org/licenses/MIT MIT
+ * @link     https://github.com/apiki/back-end-challenge
+ */
+class Router
+{
+    /**
+     * Handle the incoming request.
+     *
+     * @return void
+     */
+    public function handleRequest(): void
+    {
+        header('Content-Type: application/json');
+
+        $uri = $_SERVER['REQUEST_URI'] ?? '';
+        $uri = parse_url($uri, PHP_URL_PATH);
+        $uri = preg_replace('#^/exchange#', '', $uri);
+
+        $parts = explode('/', trim($uri, '/'));
+
+        if (count($parts) < 4 || empty($parts[0])) {
+            $this->_sendError('Missing required parameters.', 400);
+            return;
+        }
+
+        list($amount, $from, $to, $rate) = $parts;
+
+        if (!is_numeric($amount) || !is_numeric($rate)) {
+            $this->_sendError('Invalid numeric value.', 400);
+            return;
+        }
+
+        if ($from !== strtoupper($from) || $to !== strtoupper($to)) {
+            $this->_sendError('Currency must be uppercase.', 400);
+            return;
+        }
+
+        try {
+            $converter = new CurrencyConverter();
+            $result    = $converter->convert(
+                (float) $amount,
+                $from,
+                $to,
+                (float) $rate
+            );
+
+            http_response_code(200);
+            echo json_encode($result);
+        } catch (\InvalidArgumentException $e) {
+            $this->_sendError($e->getMessage(), 400);
+        }
+    }
+
+    /**
+     * Send an error response.
+     *
+     * @param string $message The error message.
+     * @param int    $code    The HTTP status code.
+     *
+     * @return void
+     */
+    private function _sendError(string $message, int $code): void
+    {
+        http_response_code($code);
+        echo json_encode(['error' => $message]);
+    }
+}
diff --git a/src/index.php b/src/index.php
index 92841bc8..df634a93 100644
--- a/src/index.php
+++ b/src/index.php
@@ -16,3 +16,5 @@
 
 require __DIR__ . '/../vendor/autoload.php';
 
+$router = new App\Router();
+$router->handleRequest();