Readability Checker

Readable writing lets the intended reader reach the main point without spending extra effort on sentence structure, unfamiliar words, or hidden assumptions. A passage can be grammatically correct and still feel heavy because it stacks several ideas into one sentence, uses long technical words without context, or expects background knowledge the reader does not have.

Readability formulas turn some of that reading load into repeatable numbers. They count surface features such as words, sentences, syllables, letters, and complex words, then estimate reading ease or school-grade level. Those estimates are useful during revision because they make patterns visible, but they do not judge truth, tone, layout, legal meaning, or whether the reader understands the subject.

Plain-language work starts with the reader and the task. A public notice, workplace update, academic abstract, legal clause, and product email can all be clear for the right audience while landing at different grade estimates. The useful question is not whether every passage reaches the same grade, but whether the intended reader can find the main message, understand the required action, and avoid a wrong interpretation.

Formula scores are strongest when they start a revision conversation. They can reveal that one oversized sentence drives a high grade, that copied slide bullets need line-aware sentence counting, or that repeated long terms should be defined instead of blindly replaced. The safer habit is to treat the score as evidence for where to reread, not as a final verdict on quality.

Audience changes the target. A grade 10 workplace update may be acceptable for trained staff, while a public notice may need a lower reading load and more direct action wording. A specialist term can be the right word when the audience knows it, but repeated technical language should still earn its place.

How to Use This Tool:

Start with the passage you plan to edit, then use the grade, ease, sentence, and word signals as a review queue. The score points to likely friction; the flagged rows show where to start rewriting.

1. Paste the passage into Text, drop a plain TXT file onto the field, or choose Browse TXT. The file path accepts plain text files and rejects files over 2 MB.
   If a file error appears, choose a smaller TXT file or paste the text directly.
2. Choose Reader target before judging the fit badge. The target changes the comparison ceiling, not the formula scores themselves.
3. Open Advanced when the text is not normal paragraph prose. Use Line-aware for sparse punctuation for bullets, notes, and slide text; use Punctuation only when line breaks should not create sentence breaks.
4. Adjust Long sentence threshold, Complex word threshold, and Long word threshold only when a style guide, grade target, or audience review bar calls for a different cutoff.
   Lower thresholds catch more rows, so they are useful for strict public-facing drafts but noisy for specialist text.
5. Add an Export label if copied tables or downloads need a draft name, page title, or version label.
6. Read Readability Metrics first for Consensus grade, Flesch Reading Ease, word count, sentence count, formula spread, and target fit.
7. Use Formula Scores when formulas disagree, then work through Revision Signals, Sentence Flags, and Word Load Flags to find the sentences or repeated terms most likely to slow readers.
8. Check Grade Formula Spread and Sentence Length Profile when you need a visual explanation of why a passage feels heavy or why a score changed after editing.
9. Confirm the result area appears before relying on copied tables, chart downloads, or JSON. If it is missing, the text field is empty or the selected file was not loaded.

Interpreting Results:

Consensus grade is the main grade estimate because it uses the median of the grade-style formulas. Flesch Reading Ease is separate because its scale runs the other way: higher ease usually means lighter reading, while lower grade estimates usually mean lighter reading.

• Fits target means the consensus grade is at or near the selected reader ceiling. It does not prove that the draft is accurate, complete, or persuasive.
• Formula spread above 4 grades means the formulas disagree strongly. Give more attention to the sentence and word tables before trusting one headline score.
• Revision Signals are editing leads. A necessary legal, medical, product, or technical term may be better defined than removed.
• Sentence Length Profile helps distinguish one or two oversized sentences from a passage that is heavy throughout.

Before treating a low grade as success, reread the draft for the real job: main point, required action, missing context, and reader knowledge. A simple score can still belong to unclear writing.

Technical Details:

Readability formulas model English prose with counts that can be estimated consistently: words, sentences, letters, syllables, complex words, and non-space characters. Sentence boundaries matter because several formulas divide words by sentence count. Syllable estimates matter because Flesch-Kincaid, Gunning Fog, and SMOG respond to word complexity. Character-based formulas such as Coleman-Liau and Automated Readability Index can move differently because they use letter or character load instead of syllable load.

The formulas cannot measure meaning, document structure, reader motivation, visual layout, or topic familiarity. They are repeatable editing indicators. A passage with one long sentence can score worse than the same passage split into shorter sentences, even when the facts are unchanged. A passage full of necessary terms can score high because the terms are long, even when the intended audience understands them.

Formula Core:

The core formulas use the same counted passage but weight the counts differently. WPS means words per sentence, SPW means syllables per word, CW means complex words, W means words, S means sentences, L100 means letters per 100 words, S100 means sentences per 100 words, LPW means letters per word, and CPW means non-space characters per word.

For a 48-word notice split into 5 sentences with 67 estimated syllables, WPS is 9.6 and SPW is about 1.40. Flesch Reading Ease becomes 206.835 - 1.015 x 9.6 - 84.6 x 1.40, or about 79.0. The same counts produce a Flesch-Kincaid grade of about 4.6, which shows why one formula should not be read as the whole writing diagnosis.

The consensus grade is the median of the five grade-style estimates: Flesch-Kincaid, Gunning Fog, SMOG, Coleman-Liau, and Automated Readability Index. Reading Ease stays separate because its scale is not a grade level. Displayed values are rounded for readability, but target-fit comparisons use the calculated values.

Rule Core:

Sentence splitting has three modes. Standard mode protects common abbreviations before splitting on punctuation. Line-aware mode lets short unpunctuated lines count as sentences, which better matches bullets and slide text. Punctuation-only mode ignores line breaks when counting sentence boundaries.

Sentence flags appear when a sentence reaches the active long-sentence threshold, has at least 25% complex words with at least two complex words, matches a simple passive-voice hint, or contains at least two -ly adverbs. Word-load flags group repeated words that reach the active long-word length or complex-word syllable threshold, then show the highest-load terms first.

English-oriented word and syllable counting creates a hard limit. Hyphenated and apostrophe forms are counted as words, syllables are estimated from letter patterns, and mixed-language text can trigger a language-mix warning when the non-ASCII letter share is high.

Limitations and Privacy:

Readability scores are editing aids. They do not verify truth, legal meaning, technical accuracy, tone, accessibility, or whether the intended reader has enough background knowledge.

• Very short text, headings, bullet fragments, and copied slide lines can produce unstable grades.
• Non-English or mixed-language passages are outside the formulas' normal English assumptions.
• Pasted text and selected TXT files are checked in the browser session rather than sent to a readability service.
• Avoid sharing the page URL after entering sensitive text, because the page state can include the entered passage.

Worked Examples:

FAQ:

Glossary:

Consensus grade

The median of the five grade-style readability formulas.

Flesch Reading Ease

A score where higher values usually mean easier reading.

Formula spread

The distance between the highest and lowest grade-style formula estimates.

Complex word

A word that reaches the active syllable threshold, usually three or more syllables.

Sentence flag

A sentence marked for length, complex-word share, passive-voice hints, or repeated -ly adverbs.

Word-load flag

A repeated or heavy word marked because it reaches the active letter or syllable threshold.

References:

• Plain language guide series, Digital.gov.
• Clear Communication Index User Guide, Centers for Disease Control and Prevention, last reviewed November 19, 2020.
• Measuring Readability, Indian Health Service.
• The Principles of Readability, ERIC, 2004.