Base64Fix.ai — Encoding Tools

URL-Safe Base64 Decoder & Encoder

Auto-detects and handles URL-safe Base64 (the variant used by JWTs, most web APIs, and OAuth). No manual conversion needed.

🔗 Decode URL-Safe Base64

Standard vs URL-Safe Base64

Standard Base64 (RFC 4648 §4) uses the characters + and / in its alphabet. These are special characters in URLs — + means space, and / separates path segments. URL-safe Base64 (RFC 4648 §5) replaces them.

PropertyStandard Base64URL-Safe Base64
Char 62+-
Char 63/_
Padding== or =Often omitted
RFCRFC 4648 §4RFC 4648 §5
Used inMIME, emailJWTs, OAuth, URLs

Where URL-Safe Base64 Appears

JWT tokens
All three parts of a JWT are URL-safe Base64 encoded (no padding).
OAuth 2.0
State parameters and PKCE code challenges use URL-safe Base64.
Google APIs
Many Google API tokens and identifiers use URL-safe encoding.
AWS signatures
Some AWS signing components use URL-safe Base64.

Converting Between Variants

// Standard → URL-safe
const urlSafe = standard
  .replace(/\+/g, "-")
  .replace(/\//g, "_")
  .replace(/=/g, "");  // strip padding

// URL-safe → Standard (for atob())
const standard = urlSafe
  .replace(/-/g, "+")
  .replace(/_/g, "/")
  + "==".slice(0, (4 - urlSafe.length % 4) % 4);

Base64Fix.ai handles this conversion automatically — just paste and decode.

Decode URL-Safe Base64 — Free

Auto-detects the variant. No manual conversion needed.

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