Add the readability calculator to your site
A free, no-account, no-API-key embeddable widget. Drop one iframe tag into your blog, knowledge base, or content tool. Light or dark mode. Six readability formulas. Zero ongoing maintenance.
Live preview
Copy-paste embed snippet
Drop this anywhere HTML works — WordPress Custom HTML block, Ghost HTML card, MDX file, plain blog post. Change the height to suit your layout.
Light or dark mode
The widget auto-detects the visitor's system preference. To force a specific theme, append ?theme=light or ?theme=dark to the iframe src:
Attribution
The widget includes a small "readabilitycheck.com" link in its footer. We ask that you keep it visible. The snippet above also includes a one-line attribution paragraph below the iframe — it is not strictly required but is appreciated and helps the project stay free.
Who this is for
- Writers and editors publishing content style guides who want readers to score their drafts in-page.
- Content marketing teams producing readability-focused educational content.
- SEO consultants embedding the tool in client deliverables and audits.
- Plain-language and accessibility advocates linking from policy pages.
- Educators teaching writing and editing — embed once, use across lesson plans.
- Healthcare and government writing teams publishing internal style guidance.
Technical notes
- The widget runs entirely client-side. The text a visitor pastes never leaves their browser.
- No API key, no account, no rate limiting.
- The widget runs on a different origin from your page, so browsers stop it from reading or changing your page.
- The widget's own files are about 21 KB before compression: one HTML page and one script. It loads no web fonts.
- It is served from Cloudflare Pages.
- The widget sets
noindexso it will not appear separately in search results. - Content-Security-Policy
frame-ancestors *means any site can embed it.
No API key, no rate limit, no signup
The embed is free forever. If you'd like a JSON API for server-side scoring (instead of an embedded widget), email [email protected] — we're prioritising features based on demand.
Frequently asked questions
Is the readability calculator widget really free?
Yes. The widget is free to embed, with no account and no API key, and it shows no ads. The main readabilitycheck.com site shows affiliate banners on some content pages. None appear inside the embed.
Do I need an API key or account to embed the widget?
No. The widget is one iframe tag. Paste the snippet into any page and it works, with no signup and no key. Text your readers paste is scored in their own browser, so we do not see or store it.
Can I switch the widget between light and dark mode?
Yes. By default the widget follows the visitor's system preference. To force a theme, add ?theme=light or ?theme=dark to the iframe source URL.
Does the widget see what readers paste?
No. The text is scored in the reader's own browser and is not sent to us. Like any web page, the widget itself is requested from our host, Cloudflare.
How tall should the iframe be on my site?
The snippet uses a height of 520 pixels. Change the height in the iframe tag if your layout needs more. The widget scales to the width of its container.
What attribution is required?
The widget has a small readabilitycheck.com link in its footer, and you cannot remove it. The snippet also adds a one-line credit below the iframe. That line is optional.