A domain can only have one SPF TXT record, but it's common to need mechanisms from several providers (Google Workspace, SendGrid, Mailchimp, and so on). Merge SPF Records combines multiple SPF strings into one valid record, removes duplicate mechanisms, and flags the problems that actually break SPF in production.
RFC 7208 requires exactly one SPF record per domain. If a mail receiver finds more than one, it's supposed to treat SPF as a permanent error and the check fails, which is worse than having no SPF record at all.
Each include, a, mx, ptr, exists mechanism, and redirect modifier costs one DNS lookup when a receiving mail server evaluates your SPF record, and RFC 7208 caps that at 10. Going over it causes the same permanent-error failure as having multiple records. This tool counts lookups in the merged result so you can catch it before it breaks email delivery.
The tool defaults to the strictest one found (-all is stricter than ~all, which is stricter than ?all), and tells you it did this, since mixing a strict policy from one provider with a loose one from another is usually a sign one of them should be tightened up anyway. You can override the choice manually.
No. You paste in the records you already have, and nothing is looked up or sent anywhere. This keeps the tool fully local, and also means it never needs network access to work.