Readability Checker (Flesch-Kincaid)
Free readability checker with Flesch Reading Ease, Flesch-Kincaid grade, Gunning Fog and SMOG scores. Highlights long sentences in your markdown.
- Flesch-Kincaid Grade
- 9
- Gunning Fog
- 12.5
- SMOG
- 12
- Coleman-Liau
- 12
- Automated Readability Index
- 9.6
- Sentences
- 7
- Words
- 99
- Avg. sentence length
- 14.1 words
- Syllables / word
- 1.62
- Long sentences
- 2 (28.6%)
- Complex words (3+ syllables)
- 17 (17.2%)
- Passive voice (est.)
- 1 sentence
Choosing a database
Most small applications should start with a managed relational database. It is boring, well documented and easy to hire for, and the operational burden was removed by the hosting provider years ago.
Teams that reach for a distributed key-value store on day one usually discover, after several months of building tooling that the managed database would have provided for free, that their query patterns were relational all along and that the migration back is far more painful than the original decision would have suggested.
Pick the simple option. Measure. Change it when the numbers say so.
What Is a Readability Checker?
A readability checker is a tool that estimates how easy a text is to read by measuring sentence length and word difficulty and converting the result into a score or a school grade level. This one reports six established formulas, Flesch Reading Ease, Flesch-Kincaid Grade, Gunning Fog, SMOG, Coleman-Liau and the Automated Readability Index, next to the raw statistics that drive them.
It also acts as a reading level checker for markdown: syntax is stripped first, long sentences are marked in the sentence view, and sentences that look passive are underlined. All processing happens in your browser.
How to Run a Readability Test
- Paste your article, README or blog post into the input pane, or open a .md or .txt file.
- Read the Flesch Reading Ease score and its label, then the consensus reading level under it.
- Scan the formula list; a grade above 12 on several of them means the text is hard for a general audience.
- Scroll to the sentence view. Marked sentences are longer than the threshold you chose in the toolbar.
- Split marked sentences, swap complex words for short ones, and rewrite underlined passive sentences.
- Watch the readability score update as you edit until it lands in the range you need.
Readability Score and Grade Level Interpretation
Flesch Reading Ease runs from 0 to 100; higher is easier. The grade formulas map directly to US school grades.
| Flesch Reading Ease | Difficulty | Grade level | Typical content |
|---|---|---|---|
| 90–100 | Very easy | 5th grade | Children's books, simple instructions |
| 80–90 | Easy | 6th grade | Conversational blog posts |
| 70–80 | Fairly easy | 7th grade | Marketing copy, product pages |
| 60–70 | Plain English | 8th–9th grade | News, most web content |
| 50–60 | Fairly difficult | 10th–12th grade | Technical documentation |
| 30–50 | Difficult | College | Academic writing, legal text |
| 0–30 | Very difficult | College graduate | Scientific papers |
The Formulas Behind the Flesch Kincaid Calculator
Every formula uses some combination of words per sentence, syllables per word, letters per word and the share of complex words (three or more syllables):
- Flesch Reading Ease = 206.835 − 1.015 × (words/sentences) − 84.6 × (syllables/words)
- Flesch-Kincaid Grade = 0.39 × (words/sentences) + 11.8 × (syllables/words) − 15.59
- Gunning Fog = 0.4 × ((words/sentences) + 100 × (complex words/words))
- SMOG = 1.043 × √(complex words × 30/sentences) + 3.1291
- Coleman-Liau = 0.0588 × L − 0.296 × S − 15.8, with L letters and S sentences per 100 words
- ARI = 4.71 × (characters/words) + 0.5 × (words/sentences) − 21.43
Sentence detection is abbreviation-aware, so “Dr. Smith” or “e.g.” do not create false sentence breaks that would make a text look easier than it is.
Why Check Readability Before Publishing
A readability checker gives you a number to argue with. If a landing page scores at college level, most visitors will skim rather than read, and support articles that score above grade 12 generate more tickets, not fewer. Run the check on drafts, fix the marked long sentences first because they move the score most, and then reduce complex words. Pair it with the sentence counter and reading time calculator linked below when you are also managing length.
Frequently Asked Questions
What is a good readability score?
For general web content aim for a Flesch Reading Ease of 60 or higher and a grade level of 8 or lower. Technical documentation for developers is usually fine at grade 10 to 12, because readers know the vocabulary. Very low scores are not automatically bad, but they do mean fewer people will finish the page.
How does the Flesch Kincaid calculator work?
Flesch-Kincaid Grade is 0.39 × (words per sentence) + 11.8 × (syllables per word) − 15.59. The readability checker splits your text into sentences, tokenises the words, estimates syllables with an English heuristic and plugs the totals into that formula and the four others listed on the page.
Why do the six formulas give different grades?
Each formula weighs sentence length and word difficulty differently: Gunning Fog and SMOG look at words with three or more syllables, Coleman-Liau and ARI use letters per word instead of syllables. The spread is normal. The consensus reading level averages the five grade formulas so you have one number to track.
Does the readability test strip markdown first?
Yes. Headings, list markers, links, images, code blocks, HTML tags and table syntax are removed before scoring, so a README is judged on its prose. Code samples are excluded entirely because they would distort sentence and syllable counts.
How is passive voice detected?
The checker looks for a form of “to be” (is, are, was, were, be, been, being) or “get” followed by a past participle, such as “was written” or “were made”. It is an estimate: sentences like “she was tired” can trigger it, and unusual participles can be missed. Use the underlined sentences as prompts to review, not as a verdict.
Is my text sent to a server?
No. The readability checker runs entirely in your browser, so drafts, internal documents and unpublished posts stay on your device.