Inspect page HTML before publishing. Find likely LCP, CLS, JavaScript, font, iframe, metadata and DOM problems, then copy practical fixes without uploading your code.
Web Performance HTML Auditor
PrivateRecommended fix order
Processing occurs in this browser. The tool does not fetch the pasted page, execute its scripts or measure real users. Keep a copy of production code and test changes on a draft page.
What the HTML performance audit checks
The audit combines preventive checks that can be evaluated safely from markup. It does not invent field measurements or pretend static HTML can reveal every runtime problem.
LCP discovery and priority
Flags a likely first image when it is lazy-loaded, hidden behind data attributes or missing appropriate fetch priority.
Layout stability
Finds images, videos and iframes without intrinsic dimensions that may contribute to layout movement.
JavaScript delivery
Reviews blocking external scripts, large inline scripts and excessive script counts that can delay interaction.
Fonts and stylesheets
Highlights render-blocking stylesheets, external font connections and missing connection hints.
DOM complexity
Reports total elements, maximum depth, large parent groups and duplicate IDs that can increase rendering work.
SEO foundations
Checks title, description, canonical, viewport and language when a complete document is supplied.
How to use the auditor
Paste the published markup
Use View Source when possible. Pasting a complete document enables metadata, resource and structure checks.
Run the performance audit
The browser parses the code locally and groups results by critical, improvement and passed checks.
Fix critical findings first
Prioritize discoverability, blocking resources, missing dimensions and loading-priority conflicts.
Verify the real page
Publish to a draft, then test with PageSpeed Insights, Chrome DevTools and field data where available.
Core Web Vitals targets and what they mean
Google's current Core Web Vitals represent loading speed, interaction responsiveness and visual stability. A page should meet all three targets at the 75th percentile, evaluated separately for mobile and desktop traffic.
| Metric | Good target | What it represents | What this tool can inspect |
|---|---|---|---|
| LCP | 2.5 seconds or less | Loading of the largest visible element | Image discovery, loading priority and blocking markup |
| INP | 200 milliseconds or less | Responsiveness across user interactions | Blocking scripts, DOM complexity and heavy inline code patterns |
| CLS | 0.1 or less | Unexpected visual movement | Missing media dimensions and unstable embed patterns |
Markup readiness is not a field measurement
The score helps you prepare cleaner code before publication. It does not claim to measure network time, server response, real interactions or layout changes created later by advertising and third-party scripts.
Performance auditing for Blogger, WordPress and custom HTML
The same performance principles apply across platforms, but the safest correction depends on how each system generates images, scripts and page markup.
Blogger pages
Audit the rendered source because the theme can add CSS, widgets and metadata beyond the editor content. Optimize Google-hosted image markup without inventing unavailable files.
Optimize Blogger image HTMLWordPress pages
Preserve image candidates generated by WordPress, then review plugin scripts, theme stylesheets, embeds and duplicated output in the final source.
Review WordPress responsive imagesCustom HTML
Inspect the complete document, verify resource loading order, and test the published result after using the suggested markup corrections.
Clean finished HTML carefullyHow the readiness score should be interpreted
The readiness score is a code-quality checklist, not a Google ranking score or a measured Core Web Vitals result.
| Score | Meaning | Next action |
|---|---|---|
| 90–100 | Markup is well prepared | Verify lab and field performance |
| 70–89 | Useful improvements remain | Review warnings and test changes |
| Below 70 | High-impact issues were detected | Resolve critical findings before publishing |
What static HTML cannot measure
INP requires actual interactions, LCP depends on network and rendering, and CLS may be caused by runtime changes. Use this tool before publishing, then confirm the outcome with real page testing. Google recommends field data for the complete experience and uses lab testing to diagnose and prevent regressions.
Methodology
The auditor parses the supplied markup with the browser's DOM parser. It does not execute pasted scripts, request external resources or upload the code. Each critical finding deducts 12 points and each improvement deducts 4 points from a 100-point markup-readiness score. Passed checks confirm only what can be observed in the supplied HTML.
The result is a preventive code review, not a measured Core Web Vitals result or a Google ranking score. After correcting the markup, test the published URL with PageSpeed Insights and real-user field data. For focused corrections, use the Responsive Image HTML Optimizer, then review the finished output with the HTML Minifier, Meta Tag Generator and Schema Validator.
Sources
- web.dev: Web Vitals. Definitions, assessment guidance and the current Core Web Vitals set.
- web.dev: Optimize Largest Contentful Paint. Practical guidance for resource discovery, loading priority and rendering delays.
- web.dev: Optimize Interaction to Next Paint. Guidance for reducing main-thread work and interaction latency.
- web.dev: Optimize Cumulative Layout Shift. Guidance for reserving space and preventing unexpected movement.
- web.dev: Browser-level image lazy loading. Appropriate use of native lazy loading and the warning against delaying above-the-fold images.
- MDN Web Docs: Web performance. Browser performance concepts and implementation references.
Frequently asked questions
Does this replace PageSpeed Insights?
No. This tool examines pasted markup before publishing. PageSpeed Insights tests a live URL and may include real-user Chrome UX Report data.
Can HTML alone measure INP?
No. INP requires actual interactions. The audit identifies blocking-script patterns and DOM complexity that may increase interaction latency.
Does a score of 100 guarantee passing Core Web Vitals?
No. Network conditions, server response, runtime scripts, advertising and user devices affect the final experience. A perfect score means only that the supplied markup passed this tool's static checks.
Can I use it with Blogger and WordPress?
Yes. Paste the rendered page source for the broadest results, or paste an article component for a focused markup review.
Does the tool upload or execute my code?
No. Parsing and analysis occur in this browser. Pasted scripts are treated as text and are not executed by the auditor.
Why are missing image dimensions important?
Width and height let the browser calculate an aspect ratio and reserve space before media loads, which helps reduce unexpected layout shifts.
Should every script use async?
No. The correct strategy depends on dependencies and execution order. Module and defer scripts preserve useful ordering behavior, while async is suited to independent scripts.
Why does the audit review the first image?
The first substantial image is a useful candidate for review, but only testing the rendered page can confirm the actual LCP element.
Should I paste editor HTML or rendered page source?
Use rendered page source when you want the most complete audit. Editor HTML is useful for checking one article or component, but it cannot reveal resources and metadata added by the theme or plugins.
Why can this audit disagree with PageSpeed Insights?
They evaluate different evidence. This tool reviews static code patterns; PageSpeed loads a live page under a test environment and may also show aggregated real-user data.
Related tools
See the full list of Developer Tools, or continue with:
- Responsive Image HTML Optimizer — prepare responsive image markup, dimensions and loading priority.
- HTML Minifier — reduce unnecessary markup after the page is verified.
- Meta Tag Generator — prepare page-specific search and social metadata.
- Schema Validator — inspect structured-data syntax before publishing.
- Robots.txt Generator — create and review crawler directives carefully.
- XML Sitemap Validator — inspect sitemap structure and URL entries.