What is Guzzle HTTP Client in PHP?

Guzzle is the most popular PHP HTTP client library, installed via Composer. It provides a clean API for making HTTP requests to external APIs and services. Basic GET request: $client = new \GuzzleHttp\Client(); $response = $client->get("https://api.example.com/users");. POST with JSON body: $client->post($url, ["json" => $data]);. It supports: async requests ($client->getAsync() returns a Promise), middleware (for logging, retrying, authentication), request options (headers, timeout, authentication), and PSR-7 request/response objects. Guzzle is used internally by most PHP SDK libraries (AWS SDK, Stripe PHP SDK, etc.) and is a standard tool for any PHP application that makes external HTTP calls.