ATS parser for ISO 14443
Decode the ISO/IEC 14443-4 Answer-To-Select (ATS) response: TL, T0, optional TA(1) / TB(1) / TC(1), and historical bytes. Useful for diagnosing reader compatibility issues.
How to use this tool
What it does
Decodes an ISO 14443-4 Answer To Select (ATS) into its capabilities and timing bytes.
When to use it
Use it when a Type A card returns an ATS and you need its frame size and protocol options.
Worked example
Parse an ATS to read the card's maximum frame size and startup frame guard time.
Input
Decoded
About ATS
ATS is the response a Type A PICC sends after a successful RATS command. It tells the reader the maximum frame size it can receive (FSC), what bit rates it supports, the frame waiting time, whether it supports CID and NAD, and any application-specific historical bytes. Most readers parse this once and cache it for the rest of the session.
Frequently asked questions
What is the ATS?
The Answer To Select: the response a Type A card returns to a RATS command, describing the frame size, timing requirements and protocol options it supports for ISO 14443-4 communication.
What does TL cover?
TL is the length byte and counts itself along with every interface byte and historical byte that follows. A TL that disagrees with the actual response length means the capture is truncated.
What are TA(1), TB(1) and TC(1)?
TA(1) advertises supported bit rates in each direction, TB(1) carries the frame waiting time and start-up frame guard time, and TC(1) indicates whether NAD and CID are supported. Each is present only if the preceding T0 says so.
Why does my ATS differ from the specification example?
Because most of it is optional. Cards omit interface bytes they have no need to advertise, and historical bytes are card-specific, so two conformant cards can return very different ATS values.
Does anything I paste leave my browser?
Nothing. The tool is entirely client-side: the page ships a static script, does no network calls, and never transmits what you paste. You can confirm it by opening the network tab, or by loading the page and then going offline.