This inquiry examined the impact of two planning conditions [the concurrent use of rehearsal and careful online planning (ROP), and the careful online planning alone (OP)] on L2 production complexity and accuracy and the ensuing evolution of these two linguistic areas in the context of text-based synchronous computer-mediated communication. Intermediate to advanced adult ESL learners (N = 33) partook in the inquiry. They completed four picture-based narrative tasks under the two planning conditions over a two-week period via text-chat. Two tasks were employed as experimental tasks to measure immediate planning effect on L2 production and the other two as new tasks to measure L2 development. Outcomes displayed that both types of planning condition backed immediate production complexity but the ROP condition was more effective in leading to more accurate use of grammatical verb forms. With regard to the ensuing evolution of production complexity and accuracy, the ROP condition was more effective in leading to improvement on clausal complexity as well as control over the use of grammatical verb forms and avoidance of general errors.