Cutting edge accuracy
Trustworthy readability algorithms verified by over 1,000 automated tests and hand-calculated scores.
We score everything – web pages, Word documents, Open Office, PDFs, Markdown and even eBooks.
Generate reports (white labelled for your clients) and have them emailed to you regularly.
URL + website scoring
Analyse an entire website, using its sitemap or RSS feed, in just a few minutes.
Email marketing scoring
Send your test email campaigns to your own unique link. We'll score them and give you a full report.
Industry leading algorithms
The world's most respected and trusted readability algorithms.
Build readability right into your website CMS or other software with our powerful API.
Monitor the sentiment and tone of your content to ensure a consistent voice.
Monitor keyword density of your content so it looks on-topic to search engines.
Make readability scoring available everywhere with our Dropbox and Slack applications.
A readability score is a computer-calculated index which can tell you what level of education someone will need to be able to read a piece of text easily.
Readable.io uses tried and tested readability algorithms, as well as our own proprietary scoring systems, to analyse the readability of your website or text and recommend ways to improve upon it.
To ensure your content is readable by 85% of the general public, you should aim for a readability score of Grade 8 or better.
Typical factors used for readability scoring include:
Flesch Reading Ease will tell you what level of education someone will need to be able to read a piece of text easily.
The Reading Ease formula usually generates a score between 0 and 100 (though scores outside of that range are possible). Unlike most of the other algorithms we use, a higher score is better when it comes to the Flesch Reading Ease.
Flesch Reading Ease is probably the most widely recognised readability scoring algorithm, and has been incorporated into law in several countries and US states as a reliable measure of readability of text.
In the mid 1970's the Flesch Reading Ease was amended so that it could be used by the US Navy. From those changes and enhancements, the Flesch-Kincaid Grade Level was created. It works in the same way, but produces a Grade Level rather than a score between 0 and 100.
Flesch-Kincaid Grade Level classifications are based on:
The Gunning Fog Index is principally used as a tool to help writers keep their texts clear and simple and was developed by Robert Gunning Associates in 1944, experienced newspapers and publishing consultants.
The Gunning Fog formula generates a grade level, typically between 0 and 20. The formula estimates the years of formal education the reader requires to understand the text on first reading.
So, if a piece of text has a grade level readability score of 6 then this should be easily readable by those educated to 6th grade in the US schooling system (i.e., 11-12 year olds).
The Automated Readability Index was developed in the 1960s by the US Air Force Medical Division as a way to analyse the readability of technical manuals, reports and training documents. Originally created to tap in to the real-world usage of typewriters to produce manuals at the time, it focusses on letter and word counting rather than syllable density.
IELTS and CEFR are related measures used by international language students to classify the profficiency of English speech. They can also be used to analyse the difficulty of a piece of text, and their scores are based on prebuilt lists of familiar words. A word like "the" will score better than a word like "xylophone", because it is used more often in English.
Developed in 1975, the Coleman-Liau Index remains one of the most commonly used readability formulas. It scores on understandability and approximates the US grade level needed to comprehend the text.
A distinctive feature of the Coleman-Liau Index is that the formula doesn't involve any counting of syllables. Instead, it was designed to easily calculate text by concentrating on characters per word.
The SMOG Index may be our favourite name of any readability score - it stands for Simple Measure of Gobbledygook, and true to its name it is based on the number of polysyllabic words in the text. Any word with three or more syllables is counted as difficult, and the density of those words in the text is what determines the SMOG score.
"SMOG should be the preferred measure of readability when evaluating consumer-oriented healthcare material." – Journal of the Royal College of Physicians of Edinburgh
The Spache and New Dale-Chall scores both work in the same way, calculating readability for a specific and narrow audience based on lists of familiar words. The greater the number of unfamiliar words in a piece of text, the worse the score. Spache is great for calculating readability scores for text aimed at children up to the fourth grade, and Dale-Chall is better suited to grades four through to ten.