What does status word 9000 mean?

SW 9000 means the command completed successfully with no further qualification. Status words beginning 61xx indicate more data is available, 6Cxx indicate a wrong Le, and 6xxx values generally signal warnings or errors.

APDU Inspector — Decode Command & Response APDUs

APDU Inspector

edit_note By the Paying.co engineering team · Updated August 6, 2026

Paste a command or response APDU and read it field by field — CLA, INS, P1, P2, Lc, data, Le, and the SW1-SW2 status word with its ISO 7816 meaning. Common EMV commands are recognised by name.

Quick answer

What is an APDU? An APDU (Application Protocol Data Unit) is the message format defined by ISO 7816-4 for communication between a smart card and a reader. A command APDU contains CLA, INS, P1, P2 and optional data; a response APDU contains optional data followed by a two-byte SW1-SW2 status word.

About APDUs

ISO/IEC 7816-4 defines the APDU as the unit of exchange between a smart card and reader. A command APDU always starts with a four-byte header — class, instruction, and two parameters — and may carry a length byte, command data, and an expected-response length. The card answers with a response APDU: optional data followed by the two-byte status word.

Command structure

CLA — class of instruction (e.g. 00 ISO, 80 proprietary)
INS — instruction code (e.g. A4 SELECT, B2 READ RECORD, AE GENERATE AC)
P1, P2 — instruction parameters
Lc — length of command data, then the data itself
Le — maximum expected length of response data

Frequently asked questions

What does 9000 mean?

Success with no further qualification. The command completed normally.

What does 61xx or 6Cxx mean?

61xx means the card has more data ready — issue GET RESPONSE with Le set to xx. 6Cxx means your Le was wrong — re-issue the command with Le set to xx.

Debugging a terminal flow?

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