3DS2 Message Builder & Decoder

Build and decode EMV 3-D Secure (3DS2) messages. Sketch an AReq from a form, or paste any AReq, ARes, CReq, CRes, RReq or Erro JSON — or a base64url creq — to get a field-by-field explanation with transStatus, ECI, reason-code and error-code lookups, all in your browser.

Follows EMV 3-D Secure Protocol and Core Functionsv2.2.0 / v2.3.1.1·verified Oct 2026· double-checked Oct 2026— value lists checked against the 2.3.1.1 Annex A text and per-version field tables, plus SDK enums; ECI values are per card scheme

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