Readability checker — Flesch score, free and in-browser

Quick answer: paste your copy and read the score, the grade level, and — more useful than either — the list of sentences that are doing the damage. Aim for 60-70 Reading Ease on ecommerce and marketing pages.

What the two numbers mean

Flesch Reading Ease runs 0-100, higher is easier:

Flesch-Kincaid grade level expresses the same underlying measurement as US school years. Grade 8 corresponds roughly to a Reading Ease of 60-70.

Why the longest-sentences list is the useful output

Both formulas take words-per-sentence as their dominant term. That means the fastest route to a better score is nearly always structural rather than lexical: split the three longest sentences and the number moves more than an afternoon of swapping synonyms would.

It also means the score is trivially gamed. A page of five-word fragments scores in the nineties and reads like a ransom note. Use the score to find the passages a reader will stall on, then fix those passages because they are genuinely hard — not to chase a target.

Where this is not the right measure

Readability formulas were built for continuous English prose. They give unreliable numbers for:

• Tables, lists and specifications, where the sentence structure is deliberately absent.
• Technical documentation, where precision legitimately requires longer words. A page explaining structured data is going to say "structured data" repeatedly, and that is correct.
• Any language other than English, since the syllable heuristics are English-specific.
• Brand and product names, which dominate ecommerce copy and get counted as ordinary vocabulary.

Readability and AI answer engines

There is a practical reason to care beyond human readers. Answer engines lift passages, and a self-contained sentence that states one fact is far more liftable than a 45-word sentence with three subordinate clauses. Writing that scores well on sentence length also tends to produce the kind of quotable, single-claim sentences that get cited — see answer engine optimization for what else makes a passage extractable.

The overlap is real but incidental. Write clearly for people; the extractability follows.