TXT Record Splitter (255-Byte Chunks)

A single DNS TXT character-string is capped at 255 bytes, because its length is stored in one byte at the front of it. That is a hard limit in RFC 1035 and not a provider policy, so anything longer — an RSA DKIM public key, an SPF record with a lot of includes — has to be published as several character-strings inside one TXT record. This tool splits the text at byte boundaries and emits the form your DNS provider expects: BIND's parenthesised ("part" "part"), space-separated quoted strings for a generic zone file, the shape Route 53 accepts, and a note where a provider splits for you.

The concatenation happens with nothing in between. A resolver hands the application the strings joined end to end, so a split may fall anywhere, including in the middle of a base64 run or halfway through a word — there is no separator to strip and no requirement that the pieces mean anything individually. Adding a space or a newline at the join, which looks tidier in a zone file, corrupts the value. DKIM specifies this behaviour explicitly, which is why a key that "looks right" in the DNS UI can still fail verification: the extra character is inside the record, not in the display.

A 2048-bit RSA DKIM key is the usual reason anyone needs this. Its public key is around 392 base64 characters before the v=DKIM1; k=rsa; p= prefix, which puts the record comfortably over 255 bytes and into two strings. A 1024-bit key fits in one, which is part of why so many DKIM records were left at 1024 bits long after that stopped being a good idea.

Two practical notes. Bytes, not characters — a non-ASCII character can take up to four bytes in UTF-8, so a 255-character limit and a 255-byte limit are not the same thing, and splitting in the middle of a multi-byte sequence produces two invalid halves. And the whole answer still has to travel: a TXT record that grows past the UDP payload limit forces a truncated response and a retry over TCP, which some restrictive networks quietly drop, so a very large record can work everywhere except one office.