This study explored the effect of two planning conditions [the simultaneous use of rehearsal and careful online planning (ROP), and the careful online planning alone (OP)] on L2 production complexity and accuracy and the subsequent development of these two linguistic areas in the context of text-based synchronous computer-mediated communication. Intermediate to advanced adult ESL learners (N = 33) participated in the study. They completed four picture-based narrative tasks under the two planning conditions over a two-week period via text-chat. Two tasks were used as experimental tasks to gauge immediate planning effect on L2 production and the other two as new tasks to gauge L2 development. Results showed that both types of planning condition supported immediate production complexity but the ROP condition was more effective in leading to more accurate use of grammatical verb forms. With regard to the subsequent development 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.