Supported regular expression syntax in AWS WAF

AWS WAF supports the regular expression pattern syntax used by the PCRE library libpcre. The library is documented at PCRE - Perl Compatible Regular Expressions.

AWS WAF doesn't support all constructs of the library. For example, it supports some zero-width assertions, but not all. We do not have comprehensive list of the constructs that are supported. However, if you provide a regex pattern that isn't valid or use unsupported constructs, the AWS WAF API reports a failure.

AWS WAF does not support the following PCRE patterns:

• Backreferences and capturing subexpressions

• Subroutine references and recursive patterns

• Conditional patterns

• Backtracking control verbs

• The \C single-byte directive

• The \R newline match directive

• The \K start of match reset directive

• Callouts and embedded code

• Atomic grouping and possessive quantifiers