HL7v2 Validator is an online tool that allows you to validate HL7v2 messages against the HL7 abstract message syntax. It is a web-based application that runs in your browser and does not require any installation.
The HL7 abstract message syntax is a special notation used to describe the structure of HL7v2 messages that lists the segment IDs in the order they would appear in the message.
In this notation, segments can be enclosed in a pair of braces to indicate one or more repetitions of the group or in brackets, to show that the enclosed group of segments is optional. If a group of segments is optional and may repeat, it is enclosed in brackets and braces. To specify that any of a group of segments can be present, angle brackets are used with vertical bars used as delimiters.
For example, the following abstract message syntax describes a message that contains a PID segment followed by an optional PV1 segment, which may repeat: