13w47c fails to launch

The game crashes after clicking play at the launcher, before showing up the mojang logo.
1.7.2 was working fine
No crash screen, no txt crash log, only these lines at the development console.
[18:59:36 INFO]: Client> Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1
[18:59:36 INFO]: Client> at com.google.gson.Gson.fromJson(Gson.java:815)
[18:59:36 INFO]: Client> at com.google.gson.Gson.fromJson(Gson.java:768)
[18:59:36 INFO]: Client> at com.google.gson.Gson.fromJson(Gson.java:717)
[18:59:36 INFO]: Client> at net.minecraft.client.main.Main.main(SourceFile:120)
[18:59:36 INFO]: Client> Caused by: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1
[18:59:36 INFO]: Client> at com.google.gson.stream.JsonReader.beginObject(JsonReader.java:374)
[18:59:36 INFO]: Client> at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:183)
[18:59:36 INFO]: Client> at com.google.gson.internal.bind.MapTypeAdapterFactory$Adapter.read(MapTypeAdapterFactory.java:145)
[18:59:36 INFO]: Client> at com.google.gson.Gson.fromJson(Gson.java:803)
[18:59:36 INFO]: Client> ... 3 more
[18:59:36 ERROR]: Game ended with bad state (exit code 1)
[18:59:36 INFO]: Ignoring visibility rule and showing launcher due to a game crash