About
A free readability calculator that actually shows its work.
Readability Check scores your writing across six published 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
Many 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 long words are marked inline, so you can see what to revise.
How it works
Text you paste and files you open are scored in your browser and are not sent to us. URL mode is the one exception: a Cloudflare function fetches the page you name and returns its text, without storing it. The six formulas are plain arithmetic in one script of about 300 lines, so results appear as you type.
Each formula is written from its published equation, not a third-party library. The sources are listed below.
Methodology & sources
Each of the six formulas comes from the source listed here:
- Flesch Reading Ease — Rudolf Flesch, "A new readability yardstick", Journal of Applied Psychology, 1948.
- Flesch–Kincaid Grade Level — Kincaid, Fishburne, Rogers, and Chissom for the US Navy, 1975. One of the two readability scores Microsoft Word shows.
- Gunning Fog Index — Robert Gunning, The Technique of Clear Writing, 1952.
- SMOG Index — G. Harry McLaughlin, "SMOG Grading: A New Readability Formula", Journal of Reading, 1969. Reviews of health readability research have recommended it for health care materials.
- Coleman–Liau Index — Meri Coleman and T. L. Liau, "A computer readability formula designed for machine scoring", Journal of Applied Psychology, 1975. It counts letters instead of syllables.
- Automated Readability Index — Smith and Senter, 1967, a report for the US Air Force (AMRL-TR-66-220). It also counts letters instead of syllables.
The syllable counter estimates syllables from spelling rules plus a short list of exceptions, and is tested against 211 words with dictionary syllable counts. Sentence splitting handles abbreviations and decimal numbers. Other tools, including Microsoft Word, can give slightly different scores because they count syllables and sentences differently.
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). One small build script assembles the pages. 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 team@readabilitycheck.com or use the contact page.