Protocol scope and method
Length conventions and framing bytes can differ between profiles. The tool reports actual bytes and both common comparison interpretations.
declaredLength = uint32BE(bytes[0..3]); compare with actual bytes.
Diagnostic scenario
Use the exact unescaped packet bytes chosen by the project framing convention. Compare the first four-byte big-endian declaration with actual byte count and document whether delimiters or check bytes are included in the selected profile.
How to interpret the result
A difference is a framing diagnostic, not proof that the sender wrote the field incorrectly. Capture truncation, escape state and different inclusion conventions must be ruled out. Report both declared and actual counts with the exact input boundary.
Input reference
- Unescaped message hex
- Example default: Sample input included
Common mistakes
- Using an unredacted production capture with vehicle, credential or network identifiers.
- Comparing an escaped wire length with an unescaped declaration.
- Treating a successfully parsed sample as standards compliance or interoperability proof.
Before using the result
- Confirm the protocol edition, transport framing and vendor profile before interpreting fields.
- Document exactly which framing and check bytes are included.
- Keep a redacted known-good and known-bad sample as a regression pair.
Questions to check during diagnosis
Does the JT/T 809 Length Validator 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.