About
A free readability calculator that actually shows its work.
Readability Check scores your writing across six industry-standard readability formulas — Flesch Reading Ease, Flesch–Kincaid Grade, Gunning Fog, SMOG, Coleman–Liau, and the Automated Readability Index — and highlights every sentence that drags the score down so you know exactly where to cut.
Why this exists
Most online readability calculators give you a number and stop there. That tells you something is wrong but not what to fix. This tool annotates your text sentence by sentence: easy ones in green, borderline ones in amber, the offenders in red. Long sentences and complex words are flagged inline so revising takes seconds, not minutes.
How it works
Everything runs in your browser. The text you paste never leaves your device — no server, no logs, no analytics on the content itself. The six formulas are pure math, computed on the client side in roughly 200 lines of JavaScript, so results appear as you type with no network round-trip.
Each formula is implemented from its original published equation, not a third-party library. The sources we used are listed below — every score on this site can be recomputed by hand from these papers.
Methodology & sources
The six readability formulas implemented here were not chosen at random. Each one is the published standard for a particular audience or context, and each has been peer-reviewed and adopted by an industry body, government agency, or major publisher:
- Flesch Reading Ease — Rudolf Flesch, "A new readability yardstick", Journal of Applied Psychology, 1948. Adopted by the US Department of Defense and Yoast SEO.
- Flesch–Kincaid Grade Level — Kincaid, Fishburne, Rogers, and Chissom for the US Navy, 1975. Default formula in Microsoft Word and many state government plain-language style guides.
- Gunning Fog Index — Robert Gunning, The Technique of Clear Writing, 1952. Widely used for business and policy writing.
- SMOG Index — G. Harry McLaughlin, "SMOG Grading: A New Readability Formula", Journal of Reading, 1969. Standard formula for healthcare and patient-information content.
- Coleman–Liau Index — Meri Coleman and T. L. Liau, "A computer readability formula designed for machine scoring", Journal of Applied Psychology, 1975. Designed to score by character count, not syllables — useful when OCR or machine-processed text is involved.
- Automated Readability Index — Senter and Smith, 1967. Originally built for typewriter-era automated grading of US Air Force technical manuals.
The syllable counter uses a deterministic algorithm tuned against the CMU Pronouncing Dictionary as a sanity check. Sentence segmentation is a regex-first approach with handling for common edge cases (abbreviations, decimal numbers, ellipses). The implementation matches the scores produced by Microsoft Word's "Show readability statistics" feature to within ±0.1 grade across reference texts.
What this tool is not
This is not a grammar checker, a style guide, or an AI writing assistant. It computes objective readability scores from established formulas. Whether a piece of writing is good depends on its audience and purpose — readability is one signal among many. The guide on target scores by audience covers the trade-offs.
Who built it
Built and maintained by Clinton Munkres, a data governance practitioner based in the United States. Day job involves regulated-document compliance — the kind of work where a fifth-grade-readable policy is the difference between something employees actually follow and something that sits in a binder. This tool started as a way to score internal policies faster, then grew into a public utility.
The code is hand-written, hosted on Cloudflare Pages, and intentionally framework-free (no React, no Vue, no build step). Total page weight is under 60KB. It is part of Boringhaus, a small portfolio of utility sites.
Citation
If you cite this tool in academic or professional writing, the suggested format is:
Munkres, C. (2026). Readability Check: A six-formula readability calculator. https://readabilitycheck.com/
Get in touch
Questions, feature requests, or bug reports go to [email protected] or use the contact page.