DNS Record Splitter
Split a long TXT value into 255-character chunks.
Paste a long DNS value, such as a DKIM public key or a long SPF or TXT record, and we will split it into the 255-character strings that DNS requires. Everything runs in your browser. Nothing is sent anywhere or stored.
This tool takes a long TXT record value and splits it into the 255-character chunks that DNS requires, so you can paste a single quoted string and get back the multi-string form your DNS provider or zone file expects. It is most useful for DKIM public keys and other authentication records whose value comfortably exceeds the limit.
Why the 255-character limit exists
A single TXT character-string in DNS can hold at most 255 bytes. That is a wire-format constraint of the protocol, not a provider quirk. When the value you need to publish is longer than 255 bytes, and a 2048-bit DKIM key encoded as p= base64 is typically around 400 characters, it has to be sent as several consecutive character-strings within the one TXT record. A resolver concatenates those strings back together with no separator, so the recipient still reads one continuous value.
How to use the output
In a BIND-style zone file you publish the chunks as multiple quoted strings on one line, for example "v=DKIM1; k=rsa; p=MIIB..." "...AB". Many hosted DNS dashboards do the splitting for you and want the raw single value pasted in one box, in which case you do not need to split at all. The important rule is that the strings must be concatenated with no spaces or characters added between them; a stray space inside the base64 will break the key. Records this affects most often are DKIM keys; SPF and DMARC values are usually short enough to need no splitting. If your DKIM still fails after publishing, validate the assembled value with the DKIM checker. If you would rather not manage records by hand at all, DMARC Engine can host and rotate them for you.
Frequently asked questions
Why does a long TXT record need to be split at all?
A single DNS TXT character-string is limited to 255 bytes by the protocol. Anything longer must be published as two or more consecutive strings inside the same record, which the resolver joins back together when it reads the value.
Will splitting change what the record means?
No. The strings are concatenated with nothing inserted between them, so the assembled value is identical to the original. Splitting is purely about fitting the wire format; the verifier sees the same continuous string.
Do I need to split my DKIM key manually?
It depends on your DNS host. Some dashboards accept the full value in one field and chunk it internally, so you paste it as-is. Others, and raw zone files, need the multi-string form. Use this tool when your provider rejects an over-length value.
Is there a limit on how many chunks a TXT record can have?
The practical limit is the overall DNS message size rather than a fixed chunk count. A 2048-bit DKIM key splits into two strings, which is fine. You should avoid unnecessarily long records, but a normal DKIM, SPF or DMARC value is never a problem.
My DKIM still fails after I split and published it. Why?
The most common cause is a space or line break accidentally added between or inside the chunks, which corrupts the base64 p= key. Re-split from the clean original and check that the strings join with no separator, then re-test with the DKIM checker.
Does this apply to SPF records too?
Rarely. SPF values are usually well under 255 characters, so they fit in one string. If yours is approaching the limit it is a sign you have too many mechanisms and should flatten or restructure it rather than rely on splitting.