Here is a list of free tools to test your website. There are tools to measure download speed, test accessibility, locate broken links, evaluate search engine and browser compatibility, and check mobile-friendliness.

Free Tests for Your Site

W3C Markup Validation Service. From World Wide Web Consortium, this validator checks the markup of web documents in HTML, XHTML, SMIL, and MathML, among others. Use other tools to validate specific content, such as RSS and Atom feeds and CSS, or to find broken links.

W3C Internationalization Checker performs various tests on a web page to determine its level of international friendliness. It also summarizes key international info about a page, such as character encoding and language declarations.

GTmetrix. Get insights on how well your site loads and recommendations on how to optimize it. GTmetrix can test your pages daily, weekly, or monthly. Set conditions based on, for example, page speed, YSlow score, page load time, and total page size, and receive email alerts on performance. Analyze the loading of your site from different regions around the world. Premium plan allows hourly monitoring.

Nibbler. Enter the address of any website and Nibbler will give you a report on key areas, including accessibility, search engine optimization, social media, and technology. Basic version is free but limited to three reports.

Screenfly. From QuirkTools, Screenfly allows you to view your website on a variety of device screens and resolutions. Enter a URL and click “Go.” Select different formats to view through the emulator.

Dead Link Checker crawls a website, identifying broken links.

Uptrends. Test your website performance in the latest browser versions using all HTML, CSS, images, and scripts. Pick your browser. Choose from worldwide regions to test from users’ locations. Select the size of the browser window used for your test and view the resulting load times. Simulate various mobile device types with a free mobile website speed test. Uptrends also offers free website monitoring.

HubSpot Website Grader evaluates website performance, including page size, page requests, page speed, and more. It also evaluates responsive design, SEO, and security.

UsabilityHub is a remote-user research platform to test your design with real people. Assess the effectiveness of navigation and content hierarchy by measuring how users complete tasks using your designs. Fine-tune visual assets, marketing copy, branding, and more, by measuring user sentiment. Free with a single user and 2-minute test time.

Five second tests. From UsabilityHub, the quick tool will help you optimize the clarity of your designs by measuring users’ recall and first impressions.

After the Deadline is a checker to receive feedback on your writing. Paste your text, and get input on contextual spell checking, advanced style checking, and intelligent grammar checking. Click the underlined text for errors, suggestions, and more options.

Readability Tests analyzes the ease of reading your text. Reading level algorithms provide only a rough guide, but they can indicate whether you’ve written content at the right level for the intended audience.

CheckMyColours is a tool for checking foreground and background color combinations of all document-object-model elements (DOM) and determining if they provide sufficient contrast for users with color deficits. All the tests are based on the algorithms suggested by W3C.

Browser Shots. Test your website’s browser compatibility in one place. Get screenshots of your web design in different operating systems and browsers from distributed computers uploaded to a dedicated server.

LambdaTest. Perform live, interactive cross-browser testing of your public or locally-hosted websites and web apps on 2,000 mobile and desktop browsers running on actual operating systems. Debug in real-time on both desktop and mobile browsers with integrated tools. Free plan for one test, five users, and up to 60 minutes a month real-time browser testing.

ClickHeat provides a visual heatmap of clicks on an HTML page, showing hot and cold click zones. ClickHeat is open source and free.

Inspectlet is a user-testing platform. It includes visitor recordings, dynamic heatmaps, A/B testing, form metrics, and error logging. Free for one website. Premium plans start at $39 per month.

Dr. Watson is a free service to analyze your web page — checking link validity, download speed, search engine compatibility, and link popularity.

Xenu’s Link Sleuth checks websites for broken links, including images, frames, plugins, backgrounds, local image maps, stylesheets, scripts, and Java applets. Link Sleuth displays a continuously updated list of URLs, to sort by various criteria.

Pingdom Website Speed Test analyzes the load speed of your website and identifies why a page is fast, slow, too big, and so on. See how your website conforms to performance recommendations from Google. Trace speed over time and from multiple locations. Pingdom offers a premium service for web speed monitoring.

Google PageSpeed Insights reports on the performance of a page on mobile and desktop devices and suggests how to improve. It provides both lab and field data about a page. Lab data is useful for debugging performance issues, but it may not capture real-world bottlenecks. Field data is useful for capturing real-world user experience but has a limited set of metrics.