Base64 Characters

The standard Base64 character set consists of 64 characters selected from the printable ASCII range. These were chosen because they are universally supported by virtually all text encodings and computer systems.

The Standard Alphabet (RFC 4648 §4)

Index	Char	Index	Char	Index	Char	Index	Char
0	A	16	Q	32	g	48	w
1	B	17	R	33	h	49	x
2	C	18	S	34	i	50	y
3	D	19	T	35	j	51	z
4	E	20	U	36	k	52	0
5	F	21	V	37	l	53	1
6	G	22	W	38	m	54	2
7	H	23	X	39	n	55	3
8	I	24	Y	40	o	56	4
9	J	25	Z	41	p	57	5
10	K	26	a	42	q	58	6
11	L	27	b	43	r	59	7
12	M	28	c	44	s	60	8
13	N	29	d	45	t	61	9
14	O	30	e	46	u	62	+
15	P	31	f	47	v	63	/

URL-Safe Base64 (Base64url - RFC 4648 §5)

In standard Base64, the characters + and / have special meanings in URL query strings and path segments (e.g. + is decoded as space, and / is a path separator). Furthermore, = is used for query parameters.

Base64url replaces these characters:

• + (index 62) is replaced with - (hyphen)
• / (index 63) is replaced with _ (underscore)
• Padding with = is typically omitted or percent-encoded