DNS TXT record splitter: how do you split a long TXT record into 255-octet chunks?

Paste the TXT value below and this tool counts its length in real UTF-8 octets, splits it into <=255-octet chunks on whole-character boundaries, and shows each chunk alongside the concatenated, correctly escaped zone-file form — entirely in your browser, with nothing you paste sent to AdminKit or anywhere else. It only reformats the text you give it: it never queries DNS, never publishes anything, and never checks whether the record you’re splitting is itself valid SPF, DKIM or DMARC syntax.

When does a TXT value actually need splitting into multiple strings?

Only once it passes 255 octets — the limit RFC 1035 §3.3.14 sets for a single <character-string> in the DNS wire format. A short SPF record or a BIMI pointer usually fits comfortably in one string and needs no splitting at all. A DKIM p= public key is the most common value to actually hit the limit: RFC 6376 §3.6.1 says plainly that “if the public key data … is long enough that it will not fit within the 255-octet limit, … it can be split into multiple strings.” AdminKit’s DKIM record generator already does this splitting for the record it builds; this tool does the same job for a value you already have from somewhere else — a key your mail provider gave you, a record you’re migrating from another DNS host, or any other long TXT string you need to paste into a zone file by hand.

Why count bytes (octets) instead of the number of characters I see on screen?

Because that is what RFC 1035’s limit actually measures. Plain ASCII text has one octet per character, so the distinction doesn’t matter for most SPF and DMARC records. It matters a great deal the moment a value contains non-ASCII text — a company name in a n= note, an accented domain, or any character outside the basic Latin set — because each of those characters can take two to four UTF-8 octets, not one. A tool that counts JavaScript string length instead of real UTF-8 bytes will under-count a multibyte value and let it through under 255 “characters” when it is already over 255 real octets on the wire.

Limits

• This tool only reformats the text you paste. It does not query DNS, does not publish anything, and has no way to tell whether the value you gave it is actually correct SPF, DKIM, DMARC, MTA-STS or TLS-RPT syntax — for that, use AdminKit’s SPF check, DKIM check or DMARC check once the record is live.
• Many DNS providers accept a long, unsplit TXT value directly in their control panel and chunk it for you automatically when they write the zone — this tool is for the cases where you’re editing a raw zone file yourself or your provider doesn’t do that chunking for you.
• Splitting is purely mechanical: it does not check that the pieces you end up with are themselves meaningful, only that each one is <=255 octets and that they concatenate back to exactly what you pasted.

Once your record is split and published, confirm it resolved the way you expect with AdminKit’s DNS lookup, or go back to whichever generator built the original value — SPF record generator, DKIM record generator or DMARC record generator — if you’re splitting a value you generated there and it already warned you a split was needed.