Protocol scope and method
This is a boundary diagnostic, not a full escape-aware stream reassembler. Confirm escaping and edition rules before trusting a candidate frame.
candidate frame = 5b ... 5d.
Common questions
Does the JT/T 809 Frame Boundary Finder leave my browser?
No application upload is used. Avoid putting sensitive production data in shareable URLs.
Is this a standards compliance test?
No. Confirm the edition and vendor profile with licensed documents and your target platform.
Offline diagnostic aid. Verify fields, version and vendor extensions before production use.