URL fragment (#) allowed characters

tl;dr

The fragment identifier component can contain:

• 0 – 9
• a – z
• A – Z
• ? / : @ - . _ ~ ! $ & ' ( ) * + , ; =
• percent-encoded characters (a % followed by two hexadecimal digits)

How can I find this out?

The URI standard is STD 66, which currently maps to RFC 3986.

In this document, you’ll find everything you need to know.

The fragment identifier component is defined in section 3.5:

fragment = *( pchar / "/" / "?" )

This means that the fragment can contain nothing or (any combination of)

• characters defined in pchar
• the /
• the ?

Definition of pchar

Refer to the appendix A. to see how pchar is defined:

pchar = unreserved / pct-encoded / sub-delims / ":" / "@"

So this adds

• characters defined in unreserved
• characters defined in pct-encoded
• characters defined in sub-delims
• the :
• the @

Definition of unreserved

Now check how unreserved is defined:

unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"

This adds

• characters defined in ALPHA
• characters defined in DIGIT
• the -
• the .
• the _
• the ~

Definition of ALPHA and DIGIT

Check how ALPHA and DIGIT are defined. They are not listed in the appendix, because they are from the core ABNF rules, as is explained in section 1.3:

ALPHA (letters), […] DIGIT (decimal digits) […]

So this adds

• a–z, A–Z
• 0–9

Definition of pct-encoded

Check how pct-encoded is defined:

pct-encoded = "%" HEXDIG HEXDIG

This allows for any percent-encoded character.

Definition of sub-delims

Check how sub-delims is defined:

sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="

This adds

• the !
• the $
• the &
• the '
• the (
• the )
• the *
• the +
• the ,
• the ;
• the =