The GTA – Move Your Alps has an extensive site with a lot of information, printable description and maps – the trail are broken down into small sections so you can tailor your trip.

grfive.com has a more in-depth description about the area, shopping, weather, currency, planning and more. It is a bit outdated but still good info

The best info is in Long distance trail. i read this blog several times and used Antti Rantanen’s GR5 Camping guide to plan my campsites along the trail.

THE GR5 TRAIL

Very good to have with you, although i was disappointed when it arrived in the mail, it was small and heavy, and i didn’t think that i would use it at all.
But i cut out the section that i was going to hike at brought that along – i ended up reading in it several times a day, especially at night when planning the next day.

“An essential guidebook for anyone walking the GR5 trail from Lake Geneva to Nice through the French Alps. The GR5 is one of the world’s most spectacular long-distance trails, yet the well graded paths make it suitable for any moderately experienced hiker or trekker. The route can be walked in a month or split over a series of summer trips.”

You can get it here: cicerone.co.uk

VIEWRANGER APP

Free app, where you can download maps. in that way you dont have to online, put your phone on “flightmode” to save enegy.
I used this extensively throughout the hike, it saved me from a few detours.

You can get it here: iTunes