How we built the Yoast SEO readability analysis

In Yoast SEO, you’ll find readability checks to help you make your text easy to read. Here, we’ll explain our choices while developing all these checks. What was our methodology, why did we include these checks in the readability analysis? And how did we set them up?

Want to know if the readability analysis works in your language? It’s available in these languages now.

Little research on what is ‘right’ in writing!

There are a lot of things we know about readability. Short sentences are easier to read than long sentences. Passive voice causes distant writing. However, linguistics is not at all an exact science. Still, we had to decide on some things to make readability checks. Which checks should we include? What should be the boundaries?

Our methodology

Why readability?

Readability is of great importance! It determines whether people understand the message of your text. Although correct spelling and grammar are important, these are certainly not the only factors influencing the readability. A readable text is a text someone wants to read through.

Deciding upon measurements

In the first stage of developing the assessments, we analyzed the competition. We decided upon the measurements of our assessments through a thorough investigation of other tools and checks. Which measurements are commonly used in grammar and spelling checks? How did these other tools measure readability?

In the second phase, we analyzed the readability of text we considered readable and on text we considered to be a bad read. In this phase, we also calculated the readability scores of text we considered well-written and the readability scores of text we considered badly written. We used all the information of the two phases in developing our content checks to come to the first version of our assessments.

Finetuning measurements with some research

In the final phase of developing the assessment, we used our readability analysis. In this phase, we put our content checks to the test. We analyzed the text of many news sites and blogs using our readability analysis tool. We checked out the text of the Guardian, of Moz, and articles from low-key mum blogs and travel blogs. We selected 75 articles from very different blogs and news sites.

Analyzing these 75 articles was to ensure that the readability analysis assessments were sufficiently distinctive. If the bullet of the readability analysis would always be green, that wouldn’t help our users. But, if it would be almost impossible to get a green bullet, that would also lead to much frustration. Our research gave us a clear overview of the readability of many different blog post.

Our research initially showed that more than 40 % of the text scored an overall red bullet on the readability analysis. It turned out that very few articles had enough transition words. We decided to lower the demands on transition words, as most articles couldn’t meet our demands. Ultimately, about 35% of the articles scored a red bullet, 30% scored an orange bullet, and 35% scored a green bullet.

After fine-tuning the assessments in this last phase, we made the final measurements of all the readability checks. We feel our instrument is useful and distinctive enough. However, if you feel otherwise, please let us know!

Read more: The readability checks in Yoast SEO: a closer look with our linguists »

The readability analysis

Below, we’ll discuss the different assessments. We’ll first explain the importance of a check and then describe the exact measurement of each assessment. Finally, we’ll discuss the measurement of the overall content score.


Most readers are lazy and quickly bored. You want to convince them to read your text in seconds. Before deciding to read your text, readers tend to scan your text. Research has shown that people generally scan a text in an F-shaped pattern. As a writer, you can guide your readers by providing them with clear subheadings. Good subheadings will not only give them a quick overview of the topics discussed, they also make the structure of your text clearly visible. Moreover, if readers decide to read your text, they’ll already know what your paragraphs will be about. This will make understanding the content much easier.

Subheadings should be equally distributed throughout your text. You should try to cover a topic in the text after each subheading. Not enough subheadings throughout your text could mean that you did not cover all your topics with a subheading. That’ll make the structure of your text less visible to your reader. Too many subheadings will make the text messy and cluttered on the other hand.

Read how the subheading check works here.


Readers like bite-sized pieces of information. Long paragraphs are scary and discourage people from reading. You should therefore make sure that paragraphs remain rather short.

Read how the paragraphs length check works here


Your sentences should not be too long either. The longer your sentences are, the harder they are to process, because readers have to keep all the words and relationships in their working memory. Therefore, in English, try to write no sentences longer than 20 words.

Read how the sentence length check works here

Transition words

Using transition words is like putting cement between your sentences. The relation between two sentences becomes apparent by the use of transition words. Readers will understand your content better if you properly use these words.

With transition words, you indicate relationships both between paragraphs as well as within paragraphs. They indicate whether a conclusion is coming up, or maybe a comparison or an enumeration. Readers can process your text more easily when they know what to expect next.

Read how the transition words check works here

Passive voice

Passive voice occurs if the noun or noun phrase that would be the object of an active sentence (such as Yoast SEO calculates your SEO score) appears as the subject of a sentence with passive voice (Yoast SEO calculates the SEO score).

Passive voice results in distant writing. Active voice is much more engaging. We discourage you from using passive voice altogether. However, some sentences get awkward when written in an active voice. That’s why we’ve set the recommended maximum percentage of passive sentences to 10%.

Read how the passive voice check works here

Flesch Reading Ease

Flesch Reading Ease measures the textual difficulty of a reading passage in English (note: in languages other than English, Flesch is unreliable). The lower the score, the more difficult the text is. The Flesch readability score uses the sentence length (number of words per sentence) and the number of syllables per word in an equation to calculate the reading ease.

Read how the Flesh Reading Ease check works here

Measurement of overall readability score

The present readability analysis of Yoast SEO contains six different content checks. These six checks are equally important in calculating the overall content score. A red bullet equals three penalty points, while an orange bullet equals two penalty points. The overall content bullet will be red if your article scores seven or more penalty points. If your article scores five or six penalty points, your article will receive an orange bullet. Articles with 0, 2, 3 or 4 penalty points will be rewarded with the much-wanted green bullet.

To score an overall green readability score, you can have one red or two orange bullets.

Coming up next!

5 Responses to How we built the Yoast SEO readability analysis

  1. Quanglepro
    Quanglepro  • 8 years ago

    Very nice…But transition words does not work with Vietnamese. So please consider to update for Vietnamese transtion words.

  2. Reiseblog
    Reiseblog  • 8 years ago

    Good to know, that you’ve also checked travel blogs. I’m curious what it will bring… I wonder how it will check foreign languages, like german…

  3. John Mulder
    John Mulder  • 8 years ago

    Maybe it is a good idea to point out which languages are supported within Content analysis. Transition word count obviously depends on the language used.

    • Marieke van de Rakt

      Thanks for you suggestion. I actually did mention that the content analysis is only available in English (for passive, transitionwords and flesch reading ease) but it was somewhere in the middle of the article. I put it in the first paragraph now.

      • Anne-Pieter
        Anne-Pieter  • 8 years ago

        Thanks Marieke, good article. Small typo in the first paragraph: Englisch