Ready to Execute
Click the blue ▶ Run button in the header bar or press Ctrl + Enter to compile and preview your results.
About Render-Blocking Resource Detector — Free Online Tool
Render-Blocking Resource Detector reads a page's HTML and lists the scripts and stylesheets that hold up the first paint.
A script counts as blocking when it has a src but no defer and no async, and is not type="module" or an ld+json data block — those are already non-blocking and are counted separately so you can see they were considered rather than missed. A stylesheet counts as blocking when it is linked and either declares no media attribute or declares all or screen; one scoped to print does not. The audit reads markup and never executes it, so a script that another script injects at runtime is invisible here, as is a stylesheet a framework adds after load.
Paste the HTML and the analysis happens entirely in your browser. Enter a URL instead and that URL goes to ShortTrick's own server to be fetched; the same parser reads the markup either way, and it is forwarded to no one else.
Finding which tag delays first paint on a landing page, checking whether a third-party snippet was added without defer, confirming a fix really removed the blocking resource, and auditing a template before it ships.
Also known as: eliminate render blocking resources · non blocking css
When to use it
Eliminating render-blocking resources is one of the highest-impact Lighthouse optimizations to improve First Contentful Paint (FCP).
How it works
Scans the <head> element for <script> tags missing async or defer attributes, and audits stylesheets for print-media swapping opportunities.
How Render Blocking Works
When the browser encounters a synchronous <script src="..."> in the <head>, it must stop building the DOM, fetch the script over the network, and execute it before continuing.
How to Use Render-Blocking Resource Detector in 4 Easy Steps
Follow this simple guide to process your files in seconds directly inside your browser tab.
Provide Input for Render-Blocking Resource Detector
Paste your payload, code snippet, or string into the Render-Blocking Resource Detector editor workspace. Performance analyzer that inspects HTML markup for synchronous scripts and stylesheets that block the browser HTML parser from rendering pixels.
Configure Formatting & Validation Rules
Select indentation preferences, minification, encoding options, or validation rules. Eliminating render-blocking resources is one of the highest-impact Lighthouse optimizations to improve First Contentful Paint (FCP).
Run In-Browser Engine
The engine executes Render-Blocking Resource Detector locally in your browser with microsecond latency and zero server transmission.
Copy or Download Output
Copy the sanitized, formatted, or generated output directly to your clipboard or download it for your project.
Why Use Render-Blocking Resource Detector on ShortTrick
Engineered for maximum speed, strict privacy, and frictionless digital productivity.
Only The URL Leaves
The address you enter is fetched by our server so the response can be read. Your own IP, cookies and headers are not forwarded, and nothing is stored afterwards.
Microsecond Performance
Optimized AST parsers and Web Crypto APIs process large payloads in Render-Blocking Resource Detector in milliseconds.
No Paywall or Account
Built for developers to use Render-Blocking Resource Detector instantly without sign-up friction or rate limits.
Syntax Validation & Formatting
Render-Blocking Resource Detector highlights syntax errors and enforces standard formatting conventions automatically.
Needs A Connection
Reaching the page under test requires the network. Pasting the page source works offline, because that path requests nothing.
Dark Mode Optimized
High-contrast typography designed for effortless reading during coding sessions.
Frequently Asked Questions About Render-Blocking Resource Detector
Common questions regarding Render-Blocking Resource Detector, data privacy, file format compatibility, and usage limits.
Related Developer Tools Tools & Popular Utilities
Explore complementary browser-based tools with zero file uploads and instant in-memory execution.
More Developer Tools Tools
Popular Tools Across Other Categories
Related Reading & Tutorials
Guides, articles, and best practices for developer tools workflows.