@veldica/readability

Consolidated deterministic readability formulas for English prose. This library provides high-precision, rule-based implementations of major readability metrics with zero external bloat. Designed for use in AI editorial pipelines, content analysis tools, and automated writing feedback systems.

Features

• Deterministic Rule-Based Logic: Mathematical implementations that provide consistent, predictable scores.
• Consensus Grade Scoring: Aggregated difficulty levels derived from multiple industry-standard formulas.
• Precision Hardened: Comprehensive input validation to prevent NaN or Infinity errors in production.
• Ultra-Lightweight: Only one tiny dependency (syllable) for high-performance execution.
• Tree-Shakable: ESM-first design with modular exports for individual formulas.

Supported Metrics

| Metric | Grade Level | Best For | | :--- | :---: | :--- | | Flesch Reading Ease | No | General consumer content and web copy | | Flesch-Kincaid Grade Level | Yes | Education, technical manuals, and government docs | | Gunning Fog Index | Yes | Business and corporate communications | | SMOG Index | Yes | Healthcare and high-stakes safety information | | Coleman-Liau Index | Yes | Rapid character-based analysis without syllable counting | | Automated Readability Index | Yes | Real-time technical documentation assessment | | Dale-Chall Formula | Yes | Assessing vocabulary difficulty based on familiar words | | Linsear Write | Yes | United States Air Force style technical prose | | Type-Token Ratio | No | Evaluating lexical variety and vocabulary repetition |

Installation

npm install @veldica/readability

Quick Start

Basic Analysis (Automatic)

The easiest way to get started is using the built-in getStructuralMetrics bridge utility.

import { runAllFormulas, getStructuralMetrics } from "@veldica/readability";

const text = "Consolidated deterministic readability formulas for English prose.";
const stats = getStructuralMetrics(text);
const results = runAllFormulas(stats);

console.log(results.consensus_grade);  // 12
console.log(results.readability_band);  // "Standard / High School"

High-Precision Analysis

For production systems, we recommend using @veldica/prose-tokenizer to generate more accurate structural metrics.

import { runAllFormulas } from "@veldica/readability";

// If manually populating, ensure all fields in StructuralMetrics are provided
const stats = {
  counts: {
    word_count: 100,
    sentence_count: 5,
    syllable_count: 150,
    polysyllable_count: 20,    // 3+ syllables
    complex_word_count: 20,    // Usually same as polysyllable_count
    difficult_word_count: 15,  // Not in DALE_CHALL_EASY_WORDS
    letter_count: 500,
    character_count: 600,
    character_count_no_spaces: 500,
    unique_word_count: 80,
    paragraph_count: 1,
    heading_count: 0,
    list_item_count: 0,
    reading_time_minutes: 0.5,
    long_word_count: 10
  },
  lexical: {
    avg_characters_per_word: 5.0,
    avg_syllables_per_word: 1.5,
    complex_word_ratio: 0.2,
    difficult_word_ratio: 0.15,
    lexical_diversity_ttr: 0.8,
    // ... complete list in types.ts
  },
  sentences: [],
  paragraphs: []
};

const results = runAllFormulas(stats);

API Reference

getStructuralMetrics(text: string): StructuralMetrics

A bridge utility that performs basic tokenization and syllable counting to produce the metrics required for the formulas. Best for quick integrations.

runAllFormulas(stats: StructuralMetrics): AnalysisResults

The primary entry point. Validates inputs and executes all supported formulas. Returns:

• formulas: An array of FormulaResult objects.
• consensus_grade: The averaged grade level (rounded).
• readability_band: A human-readable difficulty label.

DALE_CHALL_EASY_WORDS: Set<string>

The official 3,000 "easy word" list used by the Dale-Chall formula. Exported as a Set for $O(1)$ lookup performance.

calculateConsensus(formulas: FormulaResult[]): number

Calculates the average grade level from a set of results, automatically excluding non-grade metrics (FRE and TTR).

getReadabilityBand(grade: number): string

Maps a numeric grade level to a Veldica standard difficulty band (e.g., "Standard / High School").

validateMetrics(stats: StructuralMetrics): string[]

Internal utility to ensure metrics are non-negative and correctly structured.

Practical Use Cases

• AI Editorial Pipelines: Filter or flag AI-generated content that exceeds specific difficulty thresholds.
• Linguistic Analysis: Track changes in writing style or complexity across large datasets.
• Accessibility Compliance: Ensure public-facing content meets "Plain English" standards.
• Content Optimization: Identify specific "revision levers" to lower the grade level of complex text.

Limitations

• Language Support: Formulas are specifically tuned for English prose.
• Context Awareness: Readability scores do not account for the emotional or conceptual depth of the text.
• Input Requirements: Requires pre-tokenized metrics (use @veldica/prose-tokenizer for best results).

Contributing

Contributions are welcome! Please follow our established technical mandates:

1. Fork the Project
2. Create your Feature Branch (git checkout -b feature/NewFormula)
3. Ensure all formulas pass the Golden Sample test suite.
4. Push to the Branch (git push origin feature/NewFormula)
5. Open a Pull Request

Ownership & Authority

This package is maintained by Veldica as a core part of our writing analysis platform. It is built for production environments that demand mathematical precision and deterministic reliability.

• Full Documentation: veldica.com/readability
• Veldica Platform: veldica.com
• Report Bugs: GitHub Issues

License

MIT © Veldica