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RankBrain

Readability Checker

Scores how easy your text is to read and highlights the sentences and words that make it harder.

Runs in your browser. The file or text you give it is not uploaded. Free, no account.

Finding the problem is the first half.

Clear writing helps readers understand a page. RankBrain helps revise unclear copy; readability alone does not guarantee citations or recommendations.

RankBrain works on websites built in code, through the AI tool you already use (Cursor, Claude Code, Codex, ChatGPT).

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How it works

You wrote the page or the email. Now you need to know whether it reads easily or where it snags. This tool scores your text with six formulas as you type and highlights the sentences, passive constructions and long words that push the score down. Hover a highlight to see the reason.

  1. 1

    Six published formulas are calculated as you type: Flesch Reading Ease, Flesch-Kincaid Grade, Gunning Fog, SMOG, Automated Readability and Coleman-Liau.

  2. 2

    In the text itself, long sentences, passive constructions, adverbs, filler phrases and long words with a plainer alternative are highlighted.

  3. 3

    Hover over a highlight to see why it was marked.

What it does not do

  • The formulas were built for English and measure sentence and word length, not clarity of thought.

  • Passive voice and adverbs are flagged for review, not as errors.

When a source is busy or a site does not answer, this tool says so. It never fills the gap with a guess.

Questions

Which readability score should I aim for?

It depends on the reader. Flesch Reading Ease rates higher numbers easier, so aim higher for a general audience and lower for a technical one. A grade score tells you the school year a reader needs. There is no single correct target, and the formulas measure sentence length and word length, not whether your point is clear.

Why does a sentence get highlighted when it reads fine to me?

Highlighting marks what the formulas and the word lists react to: length, passive construction, adverbs, filler phrases and long words with a plainer option. Passive voice and adverbs are flagged for review, not as errors. Read the sentence again and decide. The tool shows why it marked it when you hover.

Does this work for other languages?

The six formulas were built for English, so scores for other languages are not reliable. Word and sentence length still tell you something, but the grade levels and ease scores carry no meaning outside English. Use the highlights as a rough signal and judge the rest yourself.

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