What is spintax?
Spintax is a way to write several versions of an email at once. Each {a|b|c} is replaced by one of its options when a message is sent, and braces can nest. Merge tags such as {{first_name}} fill in a value from the lead's row, and Liquid's default filter gives the text to use when that value is empty.
Reading the result
The count is exact. A brace counts the sum of its options, and braces side by side multiply, so {Hi|Hello} {there|friend} gives 4. Identical options count separately. Previews give each option an equal chance. Of Liquid, this tester reads variables and four filters: default, capitalize, downcase and upcase. Anything else, such as {% if %}, is reported as not checked. Nothing is uploaded.
Common problems it finds
A brace that never closes
A missing } leaves the brace and everything after it as literal text in every email. The tester gives the line and column where it opened.
An empty option
{Hi|} and {Hi||Hello} give some leads nothing in that place. That is sometimes on purpose, so it is a warning, not an error.
A merge tag with no data
With no value and no default, Liquid prints nothing, and the email opens "Hi ,". The previews mark each gap, and the rows section lists which rows have one.
A fallback that never runs
Liquid's default applies only to an empty value. A cell holding a single space is not empty, so the fallback is skipped. The tester counts those cells on their own.
Another tool's syntax
Sending tools differ. Instantly documents spintax as {{RANDOM | a | b}} and a fallback as {{firstName | there}}. This tester reads {a|b} and {{ firstName | default: "there" }}, and points out the other forms rather than misread them. Preview in your sending tool before launch.