Online ESL (English as a Second Language) instructors are responsible for teaching English language skills to students who speak other languages. Their main duties include preparing lesson plans, delivering lessons, assessing student progress, and providing feedback to students. The job description for an online ESL instructor may vary depending on the employer, but some common responsibilities include:

1. Creating lesson plans and course materials: Online ESL instructors must develop lesson plans and materials that are engaging, interactive, and age-appropriate for their students. They should also ensure that their teaching materials are aligned with the curriculum and learning objectives.

2. Delivering lessons: Online ESL instructors should be able to conduct live or recorded classes, using video conferencing platforms like Zoom, Skype, or Google Meet. They must be able to deliver lessons that are clear and concise, and that encourage active participation from students.

3. Assessing student progress: Online ESL instructors must assess their students' learning progress by monitoring their performance and providing regular feedback. They should also create and grade assignments, quizzes, and tests.

4. Providing feedback: Online ESL instructors must provide constructive feedback to their students, both orally and in writing, to help them improve their language skills. They must also communicate with parents or guardians regularly, providing updates on students' progress and addressing any concerns.

5. Maintaining records: Online ESL instructors should keep accurate records of their students' progress, attendance, and grades. They should also maintain records of lesson plans and teaching materials.

6. Continuing professional development: Online ESL instructors should stay up-to-date with the latest teaching methods, technology, and trends in ESL education. They should also attend professional development workshops and conferences to improve their teaching skills and knowledge.

To be successful as an online ESL instructor, candidates must possess excellent communication skills, both verbal and written. They should also have experience teaching ESL to non-native speakers, a strong understanding of ESL curriculum, and the ability to develop lesson plans and course materials. A bachelor's degree in education or ESL, as well as certification in TESOL or TEFL, is often required.