← Cloudflare Rules / rules / transform / request-header-modification / reference

Format of HTTP request header names and values

The name of the HTTP request header you want to set or remove can only contain:

• Alphanumeric characters: a-z, A-Z, and 0-9
• The following special characters: - and _

The value of the HTTP request header you want to set can only contain:

• Alphanumeric characters: a-z, A-Z, and 0-9
• The following special characters: _ :;.,\/"'?!(){}[]@<>=-+*#$&`|~^%

The maximum length of the HTTP request header value is 4 KB (~4,096 characters).