Reference, Grammar Checkers, and Text Analyzers

The original General Service List of 2000 words was created in 1953 by Michael West and this is used by most graded readers in the development of their level system.
This list includes the list of 300 sight words which cover 50~70% of most texts.
(Dolch Sight Words About   Word Lists)

The New General Service List is an updated version that includes 2818 words. It is a “list of the most important high-frequency words useful for second language learners of English, ones which gives the highest possible coverage of English texts with the fewest words possible.”Newgeneralservicelist.org

NGSL Quizlets
50 word blocks here
100 word blocks here
560 word blocks here

TestYourVocab.com

Findings:

• Most adult native test-takers range from 20,000–35,000 words
• Average native test-takers of age 8 already know 10,000 words
• Average native test-takers of age 4 already know 5,000 words
• Adult native test-takers learn almost 1 new word a day until middle age
• Adult test-taker vocabulary growth basically stops at middle age

• The most common vocabulary size for foreign test-takers is 4,500 words
• Foreign test-takers tend to reach over 10,000 words by living abroad
• Foreign test-takers learn 2.5 new words a day while living in an English-speaking country

• Native adult vocabulary size appears to be principally determined by
  reading habits between ages 4 and 15
• For native vocabulary growth, reading fiction specifically is just as important as reading in general
• Native test-taker children who read “lots” learn 4 new words a day
• Native test-taker children who read “somewhat” learn 2.5 new words a day
• Native test-taker children who read “not much” learn 1.5 new words a day