Grammar & Readability Checker

Analyze text for readability scores, word count, sentence stats, and issues.

Reviewed by the ToolNestr Editorial Team — July 2026

Flesch-Kincaid (0-100)

Gunning Fog Index

SMOG Index

Grade Level

Words

Characters

Sentences

Syllables

Avg word length

Avg sentence length

Complex words (3+ syl)

Long sentences (>40 words)

Text sections colour-coded by readability level with magnified detail view of a complex passage

How readability scores work

Readability formulas estimate text complexity based on sentence length and word difficulty. The Flesch-Kincaid Reading Ease formula scores text from 0 (very difficult) to 100 (very easy): 206.835 − 1.015 × (words ÷ sentences) − 84.6 × (syllables ÷ words). A score of 60-70 is considered plain English that most adults can read comfortably.

The Gunning Fog Index estimates years of education needed to understand text. It counts complex words (three or more syllables) and uses the formula: 0.4 × ((words ÷ sentences) + 100 × (complex words ÷ words)). A score of 12 corresponds to a high school reading level. The SMOG Index is a similar measure developed for health literacy: 1.0430 × √(30 × complex sentences ÷ sentences) + 3.1291.

Worked example

Text: "The quick brown fox jumps over the lazy dog. It was a warm summer afternoon. The sun shone brightly through the trees."

Words: 20

Sentences: 3

Syllables: 23

Flesch-Kincaid: 82.9 (Easy)

Grade Level: 5.3 (5th grade)

Gunning Fog: 6.4

Common use cases

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Website content

Ensure your web copy targets a Grade Level of 8-9 to reach the widest audience. Most adults read at this level, and simpler content improves engagement, reduces bounce rate, and makes your message accessible to non-native speakers.

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Academic writing

Academic papers typically score 30-50 on the Flesch-Kincaid scale. While some complexity is expected in scholarly work, readability tools help identify unnecessarily dense passages that could be clarified without losing precision.

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Technical documentation

Documentation should balance precision with clarity. Use readability scores to spot sections that are harder to read than necessary. Aim for a Flesch-Kincaid score above 40 for general technical docs, and above 60 for end-user guides.

What the readability checker detects

The tool analyses your text for several potential readability issues. It counts complex words (those with three or more syllables) which tend to make text harder to read, and highlights them with an underline so you can review each one. Long sentences (over 40 words) are highlighted in yellow as they often signal run-on constructions or overly complex ideas that could be split into shorter, clearer sentences.

Beyond sentence and word analysis, the tool also calculates your average word length and average sentence length, giving you baseline metrics to track improvements. The syllable count helps identify dense vocabulary: English text with an average syllable count above 1.8 per word is considered complex. By monitoring these metrics over time, you can develop a clearer, more accessible writing style that communicates effectively with your intended audience.

While this tool does not perform full grammatical analysis (it will not catch subject-verb agreement errors or misplaced modifiers), it provides a strong quantitative foundation for understanding your text's readability profile. Combined with careful proofreading and an understanding of your audience's needs, the readability scores and highlighted feedback give you actionable insights for improving your writing.

Tips for improving readability

Short sentences improve readability

Aim for an average of 15-20 words per sentence. If a sentence exceeds 40 words, consider splitting it into two or three shorter ones. Shorter sentences are easier to parse and reduce cognitive load on the reader. The tool highlights sentences longer than 40 words in yellow so you can spot them quickly.

Simple words score better

Replace multi-syllable words with shorter alternatives where possible. For example, use "use" instead of "utilize", "help" instead of "facilitate", and "show" instead of "demonstrate". Complex words (three or more syllables) significantly lower readability scores and can make text feel formal or academic.

Write for your audience

There is no single perfect readability score. General web content should target Grade Level 8-9 (Flesch-Kincaid 60-70). Marketing copy can target 70-80 for broad appeal. Academic and technical content will naturally score lower (30-50), which is appropriate for specialist audiences who expect complexity.

Avoid passive voice

Passive constructions like "the report was written by the team" are longer and harder to read than active alternatives like "the team wrote the report." Passive voice also tends to create longer sentences by adding extra words without adding meaning.

Use transition words carefully

Transition words like "however", "therefore", "nevertheless", and "consequently" are useful for showing relationships between ideas, but overusing them can increase sentence length and complexity. Use transitions sparingly and prefer simple connectors like "but" and "so" where appropriate.

Understanding your results

When you paste text into the tool, the scores update live as you type. The Flesch-Kincaid Reading Ease score is the most intuitive: it ranges from 0 to 100, with higher scores indicating easier readability. A score of 60-70 is considered "standard" and is appropriate for most general audiences. Below 30 is "very difficult" and typical of legal or scientific documents. Above 80 is "easy" and suitable for children's content or simplified instructions.

The Grade Level score estimates the US school grade required to understand the text. A score of 8 means an eighth grader (around 13-14 years old) can comfortably read the text. Most newspapers aim for grade level 8-10, while academic journals may target grade 12-16. The Gunning Fog Index works similarly, with 12 being high school level and 17+ being university graduate level.

The highlighted view below the scores shows your text with visual markers: sentences over 40 words have a yellow background, and complex words (three or more syllables) are underlined. This makes it easy to scan your text and identify specific areas that may need rewriting, without having to read through every score in detail.