YSlow
Analyzes web pages and why they're slow based on Yahoo!'s rules for high-performance web
YSlow is a web performance analysis tool that examines web pages and identifies why they are slow, based on Yahoo!'s rules for high performance web sites. It grades a page against one of three predefined rulesets or a user-defined ruleset, offers suggestions for improving performance, summarizes the page's components, and displays statistics about the page.
The tool includes performance analysis utilities such as Smush.it and JSLint. Its analysis covers 23 testable rules drawn from a set of 34 web performance best practices, addressing areas like HTTP requests, caching, compression, script and stylesheet placement, DNS lookups, redirects, cookies, and image handling. YSlow is available across several platforms, including Firefox, Chrome, Opera, Safari, a mobile bookmarklet, command line (HAR), PhantomJS, and Node.js, with source code available.
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