A detailed look at the formulas, algorithms, and rules that power BullSwift text analysis tools.
The BullSwift readability checker calculates multiple readability metrics using established formulas that have been validated across millions of documents. The primary metric is the Flesch Reading Ease score, which measures how easy text is to understand.
206.835 - 1.015 × (total words / total sentences) - 84.6 × (total syllables / total words)This formula produces a score between 0 and 100, where higher scores indicate easier readability:
0.39 × (total words / total sentences) + 11.8 × (total syllables / total words) - 15.59This formula converts readability into a U.S. school grade level. A score of 8.0 means the text is suitable for an 8th-grade student. Most web content targets a grade level between 6 and 8 for maximum accessibility.
Learn more about interpreting these scores in our Flesch Reading Ease guide and readability score recommendations.
The keyword density checker calculates how frequently specific words or phrases appear in your content as a percentage of total words. This metric helps ensure balanced keyword usage for SEO without over-optimization.
Keyword Density (%) = (Keyword Occurrences / Total Words) × 100For example, if a keyword appears 15 times in a 1,000-word article:
(15 / 1000) × 100 = 1.5% keyword densityBullSwift analyzes both single keywords (unigrams) and multi-word phrases (bigrams, trigrams). The tool automatically filters common stop words like "the," "and," and "is" to focus on meaningful content words.
SEO best practices recommend keeping primary keyword density between 1-2% for most content. Densities above 3% may trigger search engine over-optimization filters. Learn more in our keyword density recommendations.
BullSwift tools analyze text structure by detecting sentence and paragraph boundaries. This analysis powers multiple features including the sentence counter, paragraph counter, and structural metrics in the readability checker.
Sentence Boundaries
Sentences are detected using punctuation analysis that identifies terminal punctuation (periods, question marks, exclamation points) while correctly handling abbreviations, decimal numbers, and other edge cases.
Paragraph Boundaries
Paragraphs are identified by line breaks and whitespace patterns. Double line breaks typically indicate paragraph separation, while single line breaks within text are treated as soft wraps.
Average Calculations
Average sentence length is calculated as total words divided by total sentences. Average paragraph length uses total words divided by total paragraphs. These metrics help identify overly long or short structural elements.
Well-structured content typically uses sentences averaging 15-20 words and paragraphs of 3-5 sentences for web readability. Our tools flag sentences exceeding 30 words and paragraphs exceeding 150 words as potentially difficult to read.
Use BullSwift tools to analyze your writing using these proven methodologies.