As websites, web applications, APIs and services become more and more critical, it’s import to design and build applications so that they scale well for a large number of requests. To actually test and verify the behavior of services under load, testers and developers can perform load and stress tests. For web applications a load test would usually involve defining, writing and running test scenarios.

A test scenario could be a script that simulates the behavior of a typical user across multiple pages of a website or web application. Once you defined your test scenarios, you can execute it by simulating many concurrent virtual users and monitor how your application behaves. Likewise for APIs and other services, the idea is to generate requests that are as realistic and similar to the possible load of your production environment, so you can optimize and scale your application and services based on accurate and realistic data.

There are various tools that you can use to build, conduct and analyze load and stress tests for web applications and other services. Most tools require that you build test scenarios, usually scenarios a typical user would perform on a website, and then simulate many virtual users simultaneously.

JMeter

JMeter is an open source Java-based load and performance testing tool. Besides testing web applications and services, you can also load test other services such as LDAP, mail servers or databases.

Tsung

Tsung is an open source multi-protocol distributed load testing tool. The purpose of Tsung is to simulate users in order to test the scalability and performance of services, such as HTTP servers and other services.

ApacheBench

This is a tool for benchmarking your HTTP server. It is designed to give you an impression of how your current Apache (or other web server) installation performs. This especially shows you how many requests per second your Apache installation is capable of serving and can be useful to benchmark web applications and APIs as well.

Locust

Locust is a scalable and distributed load testing tool for web applications, websites and web-based services. Locust comes with a web-based user interface and allows you to write test scenarios in Python.

WAPT

WAPT is a load and stress testing tool that allows you to build, generate and monitor load tests via a graphical user interface. WAPT comes in two editions and doesn’t limit the number of virtual users you can use like most other commercial tools do.

Webserver Stress Tool

The Webserver Stress Tool is an advanced load testing tool that comes with a graphical user interface to run and analyze your load tests. This tool can generate a number of different tests to verify your web applications and services.

LoadUI

LoadUI is a cross-platform load and stress testing tool. LoadUI is available as both open source and commercial editions. Its UI allows you to create, configure and redistribute your load tests interactively and in real-time.

Loadster

Loadster it a load and stress testing tool specifically designed for high-performance web applications. It comes in two parts: a tool to build and design your test scenarios, and an engine that you can use to actually run and distribute your load tests.

Source: http://www.testingtools.com/load-testing/