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Base64 encoder & decoder

Turn text into Base64 and back, with each byte’s path to a Base64 letter shown bit by bit.

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Runs in your browser. Nothing you paste is sent anywhere.

How it works

3 bytes → 4 letters

Text is first turned into bytes (UTF-8: plain letters take one byte, “☕” takes three). Base64 then takes the bytes three at a time, 24 bits, and cuts them into four 6-bit pieces. Each piece is a number from 0 to 63, and that number picks a letter from the 64-character alphabet below. Here are your first bytes going through it:

  1. Why it’s about a third bigger every 3 bytes → 4 characters, so size × 4 ÷ 3 (rounded up to a multiple of 4)
  2. Padding 1 byte left over → 2 letters + “==”, 2 bytes left over → 3 letters + “=”

The Base64 alphabet

RFC 4648
  • 0A
  • 1B
  • 2C
  • 3D
  • 4E
  • 5F
  • 6G
  • 7H
  • 8I
  • 9J
  • 10K
  • 11L
  • 12M
  • 13N
  • 14O
  • 15P
  • 16Q
  • 17R
  • 18S
  • 19T
  • 20U
  • 21V
  • 22W
  • 23X
  • 24Y
  • 25Z
  • 26a
  • 27b
  • 28c
  • 29d
  • 30e
  • 31f
  • 32g
  • 33h
  • 34i
  • 35j
  • 36k
  • 37l
  • 38m
  • 39n
  • 40o
  • 41p
  • 42q
  • 43r
  • 44s
  • 45t
  • 46u
  • 47v
  • 48w
  • 49x
  • 50y
  • 51z
  • 520
  • 531
  • 542
  • 553
  • 564
  • 575
  • 586
  • 597
  • 608
  • 619
  • 62+
  • 63/

Good to know

  • Base64 is an encoding, not encryption: anyone can decode it. Don’t use it to hide passwords.
  • You’ll see it in email attachments, data: URLs for images, and the middle part of login tokens (JWTs).