Performance-Bookmarklet
A bookmarklet and browser extension that analyzes web page performance using the Resource Timing, Navigation Timing, and User-Timing APIs.
What is Performance-Bookmarklet?
Performance-Bookmarklet is a browser-based tool that analyzes web page performance using the Resource Timing, Navigation Timing, and User-Timing APIs. It provides visualizations and metrics for resource loading, navigation events, and custom performance marks, helping developers identify and fix performance bottlenecks directly in the browser.
Frontend developers, web performance engineers, and QA testers who need to quickly analyze and optimize page load times and resource efficiency during development.
It offers a lightweight, immediate alternative to external performance testing tools by running directly in the browser, providing detailed insights without requiring complex setups or external services.
Overview
Performance-Bookmarklet helps to analyze the current page through the Resource Timing API, Navigation Timing API and User-Timing - requests by type, domain, load times, marks and more. Sort of a light live WebPageTest.
Use Cases
Best For
- Quickly identifying slow-loading resources during development
- Analyzing third-party script impact on page performance
- Debugging navigation timing issues like DNS lookup or connection delays
- Visualizing User Timing API marks and measures for custom performance tracking
- Comparing request distribution by domain and content type
- Getting a lightweight, in-browser alternative to WebPageTest for initial performance checks
Not Ideal For
- Sites with strict Content Security Policy directives that block bookmarklets
- Teams needing comprehensive performance testing with network throttling or device simulation
- Projects requiring server-side performance analysis or backend monitoring
- Environments with browsers that don't support modern timing APIs (e.g., older Internet Explorer versions)
Pros & Cons
Pros
It runs directly in the browser without external setups, providing instant feedback on page performance using built-in timing APIs like Resource Timing and Navigation Timing.
Offers detailed navigation and resource timing waterfalls, pie charts for domain analysis, and tooltips for precise metrics, making data interpretation straightforward.
Available as a bookmarklet, Chrome extension, and Firefox add-on, ensuring flexibility across different browsers and usage scenarios, as highlighted in the README.
Integrates with custom performance marks and measures, allowing developers to track specific application events alongside standard metrics for enhanced debugging.
Outputs structured data tables to the console for deeper analysis and supports persisting metrics across page refreshes, aiding in continuous performance monitoring.
Cons
The bookmarklet version can be blocked by Content Security Policy directives, requiring fallback to extensions or manual script pasting, which adds friction, as admitted in the README.
Only analyzes data available through Resource Timing and Navigation Timing APIs, so it may miss server-side performance issues or advanced metrics like Core Web Vitals without additional setup.
Lacks capabilities like network throttling, device emulation, or automated testing runs, making it less suitable for comprehensive performance profiling compared to full-fledged tools like WebPageTest.
Open Source Alternative To
Performance-Bookmarklet is an open-source alternative to the following products:
Frequently Asked Questions
Related Projects
PerfMapFront-end performance heatmap bookmarklet.
DOM MonsterA cross-platform, cross-browser bookmarklet that will analyze the DOM & other features of the page you're on, and give you its bill of health
CSS StressCSS Stress is a Testing and Performance Profiling
Yahoo YSlow for Mobile/BookmarkletYSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high-performance web pages
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