The plasma edge MHD stability is analysed for several JET discharges in the diagnostic optimized configuration. The stability analysis of Type I ELMy plasmas shows how after an edge localized mode (ELM) crash the plasma edge is deep in the stable region against low- to intermediate-n peeling–ballooning modes. As the pressure gradient steepens and the edge current builds up, the plasma reaches the low- to intermediate-n peeling–ballooning mode stability boundary just before the ELM crash. Increasing the plasma fuelling by gas puffing makes the second stability access against high-n ballooning modes narrower until it closes completely and theELMschange fromType I toType III. Reducing the plasma heating has a similar effect. Increasing the safety factor at the plasma edge improves the stability against low- to intermediate-n modes allowing steeper pressure gradients to develop before an ELM crash.