There are several tools to test and optimize website performance:
LoadStorm − Developers can use this tool to check the loading time of the website. The tool allows users to create as many test plans, scenarios and steps as needed. The tool allows tests to be built to simulate a large number of different users with unique logins and different tasks.
SiteAnalysis − This tool can be used to test and validate key components of a website. It helps to test and verify internal and external links, domain names, DNS servers and SSL certificates. This can be done hourly or weekly as needed.
Avalanche – Another load testing tool specially designed for testing the security, networking and web application infrastructure by generating large amounts of user and network traffic. It works with multiple web browsers, supports web service testing, supports HTTP 1.0/1.1, SSL, FTP, RTSP/RTP, MS Win Media, etc.
VisualVM – This free tool helps test Java applications. It automatically detects and lists Java applications running locally and remotely while monitoring application performance and memory consumption.
HTML Validator – This add-on from Mozilla adds HTML validation to Firefox and Mozilla. It can indicate the number of errors of the HTML page, shown as defects in the status bar. Users can easily see error details in the HTML source of the page for correction.
Fortify 360 – This is a security and vulnerability detection tool for websites. It features integrated static source code analysis, dynamic runtime analysis, and real-time monitoring to identify and accurately prioritize the largest number of critical security vulnerabilities.
XenoCode Browser Sandbox – This is an essential testing tool for developers to run browser tests before launching a website. The tool offers a suite of virtual applications that can run all popular browsers at the same time. No software even needs to be installed.
W3C HTML Validation Service – This validator checks HTML, XHTML, SMIL, MathML, etc. web documents for markup validity. If you need to validate specific content, such as RSS/Atom feeds or CSS stylesheets, MobileOK content, or find broken links, other validators and tools are available.
Google’s Website Optimizer – Google’s testing service that allows users to test the desired content and pages. Usually used to test headlines, images, or text using web-based systems. Testing helps analyze the impact on conversions, user actions, traffic, or other goals.
DeviceAnywhere – This mobile handset testing tool facilitates the development, deployment and testing of content over the Internet on more than 2000 real handsets in a real-time global network around the world.
I hope these tools help freelance web developers develop a user-friendly and error-free website. Share your suggestions and feedback.