Is Base64URL more secure than Base64?

No. Only the alphabet changes. Both are encodings. Security comes from TLS, signatures or encryption elsewhere.

Can I strip the = characters?

Often yes for Base64URL consumers. Restore padding before a strict Base64 decoder if it requires a multiple of four.

Why does my decode fail with “invalid character”?

You are feeding Base64URL into a standard decoder (- and _), or the other way around. Switch alphabet, or replace -→+ and _→/ then pad.

Base64 vs Base64URL, and why strings end in =

Base64 turns bytes into ASCII. Base64URL is the same idea with a URL-safe alphabet. The trailing = characters are padding, not encryption, and some systems strip them.

What the alphabet is

Standard Base64 uses A–Z, a–z, 0–9, + and /, and pads with = so the length is a multiple of four.

Base64URL (RFC 4648 §5) swaps + for - and / for _. That avoids breaking query strings and file paths. JWTs, many signed cookies and some cloud signed URLs use Base64URL.

Why strings end in =

Base64 encodes three bytes as four characters. If the input length is not a multiple of three, the encoder adds one or two = characters so the output length stays a multiple of four.

One leftover byte → two padding chars (==). Two leftover bytes → one (=). Zero leftover bytes → no padding.

echo -n "ab" | base64
# YWI=   (2 bytes → one =)

echo -n "a" | base64
# YQ==   (1 byte → two =)

When padding is optional

Some protocols (JWT header and payload, many Base64URL APIs) omit padding. Decoders usually accept both. Encoders that must match a strict verifier should keep the same padding rule the verifier uses.

If a library rejects a JWT segment, try adding = until the length is a multiple of four before decoding.

Choosing the right mode

Use standard Base64 for MIME, data URLs, and most “encode this blob” tasks.
Use Base64URL when the string will sit in a URL, filename, or JWT.
Do not call either encryption. Anyone can decode them.

Questions

Is Base64URL more secure than Base64?: No. Only the alphabet changes. Both are encodings. Security comes from TLS, signatures or encryption elsewhere.
Can I strip the = characters?: Often yes for Base64URL consumers. Restore padding before a strict Base64 decoder if it requires a multiple of four.
Why does my decode fail with “invalid character”?: You are feeding Base64URL into a standard decoder (- and _), or the other way around. Switch alphabet, or replace -→+ and _→/ then pad.