Free · no install · current 2024 standard
Free SAE J2735 decoder and message creator
SPaT, MAP, TIM, BSM, RSM work zones, SDSM and 40 more message types, decoded and built on the current SAE J2735_202409 standard — with IEEE 1609.2/1609.3 unwrapping, a human-readable summary, a map, and NTCIP 1218 push to your own roadside units.
Decode a packet
Paste hex, base64, XER or JSON from a capture or a vendor log. Whole Ethernet, WSMP and IEEE 1609.2 frames are unwrapped automatically.
Open the decoder →Create a message
Start from a validated template, edit the JSON or the quick fields, and get constraint-checked UPER hex ready for your RSU.
Open the creator →Register your RSU
Free account: 500 operations a day, an RSU registry with encrypted SNMPv3 credentials, and one-click NTCIP 1218 push.
Create a free account →What it does
Everything between the air interface and the engineer
Auto-detects wrappers and revisions
Ethernet II 0x88DC → IEEE 1609.3 WSMP → IEEE 1609.2 SPDU (signed or unsecured) → J2735 MessageFrame, with every layer shown. Captures from 2016, 2020 and 2024 devices are matched to their own J2735 dictionary.
Constraint-checked encoding
Every encode is validated against the J2735_202409 ASN.1 constraints, so an out-of-range lat/long or a wrong bit-string length is caught before it reaches a vehicle.
Summary and map
Positions, speeds, signal states, ITIS phrases and lane geometry rendered in engineering units, with lanes, paths and regions plotted on a map.
NTCIP 1218 push
Send a message to your own RSU over SNMPv3 (store-and-repeat or immediate forward) with PSID, channel, interval and delivery window.
SCMS and FCC guides
Plain-language guides to SCMS enrollment, FCC C-V2X licensing under 24-123, and NTCIP 1218 configuration — written for agencies, not vendors.
JSON API
Decode, encode, templates, random examples and RSU push from your own scripts and dashboards. CORS-enabled, documented with curl examples.
Built for agencies and integrators
Verify what your RSUs are really broadcasting
Acceptance testing a connected intersection, checking a vendor's SPaT/MAP against CTI 4501, debugging a TIM that never shows on the OBU, or drafting an RSM work-zone message before the crews arrive — paste the bytes, read the result, fix the field, re-encode.
- All 50 J2735 2024 message types and 1,218 schema types, including J2945/4 RSM and J3224 SDSM
- Templates with real Northern Virginia geometry you can edit in place
- Reproducible share links for tickets and emails
- Free for anonymous use (5 decodes/day) and free accounts (500/day)
Managed RSU service
Want ITS Roads to manage your RSUs, SCMS enrollment and message generation? Free registration here; dedicated managed service by contract.
Talk to ITS RoadsWhy trust it
The codec is compiled from the USDOT asn1c-generated J2735_202409 code and round-trip tested (JSON → UPER → JSON) across all 1,218 types. Every template on this site was encoded, decoded and compared for equality before publishing. Interpretation rows are best-effort and never block a decode; the JSON tab always shows the exact decoded structure. Decodes captures from SAE J2735 2016, 2020 and 2024 devices (auto-detected), encodes on the current 2024 revision, and is built to add the 2026 revision alongside when SAE publishes it.
Standards: SAE J2735_202409 (Sept 2024) — V2X Communications Message Set Dictionary; J2945/4 RSM and J3224 SDSM modules included · IEEE 1609.2 (security services; 1609.2-2025 published Oct 2026) — SPDU unwrapping · IEEE 1609.3-2020 + Cor 1-2024 — WSMP networking header · NTCIP 1218 v01 — RSU object definitions used for message push