The Readability Scores Your Content Tool Is Missing

Most readability tooling stops at a single score. That is a problem if you are building a documentation pipeline, a content linter, or any system that needs to catch unreadable text before it ships.

Here are the four metrics worth tracking, what each one actually measures, and what your targets should be.

Flesch-Kincaid Grade Level

This score maps text to a U.S. school grade level based on two inputs: average sentence length and average word length in syllables. A score of 8 means a typical 13-year-old can read it without friction.

Target: 6 to 9 for most technical docs.

If your score is above 12, sentences are too long or you are leaning on polysyllabic jargon. Users will skim past dense paragraphs instead of reading them. If your score is below 5, you are likely oversimplifying to the point where context is missing.

Flesch Reading Ease

This uses the same inputs as FK Grade Level but outputs an inverse score on a 0 to 100 scale. Higher means easier. It weights sentence length more heavily than syllable count, so it punishes run-on sentences hard.

Target: 60 to 70 for technical documentation.

Below 50 and you are in academic or legal territory. Most readers will not finish the section. Above 75 and you may be losing precision, which matters in technical writing where exact phrasing carries meaning. The 60 to 70 range is the practical sweet spot where clarity and accuracy coexist.

Automated Readability Index (ARI)

ARI takes a different approach. Instead of counting syllables, it counts characters per word. This makes it faster to compute and less sensitive to syllabification edge cases. It outputs a grade-level score similar to FK but often diverges on technical content, where long words are common but not necessarily difficult for the target audience.

Target: 7 to 10 for developer docs.

Where ARI earns its place is as a cross-check. If FK says grade 8 but ARI says grade 14, you likely have a cluster of long technical terms inflating the character count. That is worth reviewing even if the content reads fine to a subject matter expert, because new users will not have that context.

Sentence Length Variance

Most tools report average sentence length and stop there. Variance is the signal they miss. Text where every sentence is roughly the same length reads as monotonous and is harder to parse. Alternating short and long sentences creates rhythm, which keeps readers oriented.

Target: Standard deviation of 8 to 15 words across your sentence lengths.

Below 5 means your writing is flat. Above 20 means sentence structure is inconsistent in a way that will confuse automated parsers and human readers alike. This is especially relevant in procedural docs where scannable short sentences should anchor longer explanatory ones.

I built a TextAnalytics API that returns all of these scores in a single call -- useful if you are building a linter, a CMS plugin, or just want to quality-gate your content pipeline: https://rapidapi.com/hummusonrails/api/textanalytics