ESP8266 Community Forum

According to one person having contact with the developers, developers use their own private compiler, but will soon switch to gcc and lay out everything you need.

Just my luck, I had just converted and reformatted the Chinese version myself
https://www.dropbox.com/s/cpzs2qqa6sdb0fe/ESP8266DataSheetEnglish-PBJ.pdf?dl=0

Doesn't matter, I will use this new document to jazz up my version too!

Under section 8.4.4 it seems to indicate the GPIO pins are [edit: not] 5V tolerant!
Thats handy...

I had accidentally powered a board briefly with 5V with no damage...

I should add this is just a guess - don't fry your board based on this post.

nitto wrote:Under section 8.4.4 it seems to indicate the GPIO pins are 5V tolerant!

NO. The table explicitly lists that the maximum allowable voltage at any GPIO pin is 3.6V. Any higher voltage is therefore outside the recommended operating conditions. Nowhere is specified nor guaranteed that the device will operate correctly under an over-voltage condition. Operating a device outside its recommended operating conditions may, sometimes severely, shorten the life-span of a device.

You must have been tricked by this paragraph:

All digital IO pins are protected from over-voltage with a snap-back circuit connected between the pad and ground. The snap back voltage is typically about 6V, and the holding voltage is 5.8V. This provides protection from over-voltages and ESD. The output devices are also protected from reversed voltages with diodes.

Over-voltage protection is there to protect the part from failing immediately in case of an incidental over-voltage condition, not to just make the inputs tolerant to sustained over-voltage.