Aztec Code

Aztec is the 2D barcode on every airline boarding pass, almost every rail-ticket app, and a growing share of transit fareplates. It's the one 2D symbology specifically optimised to decode reliably from a low-contrast phone screen behind a thumb smudge — which is why IATA chose it for the BCBP (Bar Coded Boarding Pass) standard in 2005 and never moved.

Canonical spec: ISO/IEC 24778:2008 — Information technology — Automatic identification and data capture techniques — Aztec Code bar code symbology specification.
IATA application: BCBP (Bar Coded Boarding Pass) Resolution 792 — defines the Type M1 payload format every airline uses.
Originator: Welch Allyn (now Honeywell), 1995. Royalty-free since the original patent expired.

What it is

A square matrix code with a distinctive bullseye finder pattern in the centre (concentric squares), surrounded by data modules arranged in a spiral. Unlike QR, Aztec has no position/alignment patterns in the corners — the centre bullseye is the only fiducial, which means Aztec tolerates rotation, off-centre framing, and non-square cropping much better than QR.

Five properties that make Aztec unusually good for display-on-screen scanning:

No quiet zone required. QR needs a 4-module margin; Aztec decodes with zero. Useful when a phone screen's edge or bezel crops into the code.
Bullseye finder tolerates contrast loss. Phone LCDs at low brightness, sun glare, oleophobic-coating smudges — Aztec survives all three where QR's three corner markers wash out.
Variable ECC 5%–95%. QR has 4 levels (L/M/Q/H) capping at 30%. Aztec goes to 95% error correction for extreme-damage scenarios.
Compact relative to capacity. At 3,067 alphanumeric chars maximum, Aztec packs more in a smaller footprint than PDF417 or Data Matrix.
No orientation lock. QR requires the finder patterns to resolve orientation; Aztec's bullseye is rotationally symmetric.

Size and capacity

Variant	Dimensions	Max alphanumeric capacity	Typical use
Compact	15 × 15 to 27 × 27 modules	~110 chars	Short URLs, IATA seat assignments
Full-Range (small)	19 × 19 to 45 × 45	~400 chars	BCBP Type M1 boarding passes
Full-Range (medium)	49 × 49 to 95 × 95	~1,200 chars	Transit tickets with multiple segments
Full-Range (max)	151 × 151	~3,067 chars	Heavy payloads — rare in practice

Error correction levels

Aztec ECC is specified as a percentage of the data codewords dedicated to Reed-Solomon correction. The generator accepts any value from 5% to 95%; defaults are 23% (matches QR level M) for general use and 50% for boarding passes / transit tickets.

ECC level	Typical use	Tradeoff
5%	Experiments / demos only	Fails on any real-world damage. Never ship production codes at this level.
23% (default)	Short-URL Aztec on digital displays	Matches QR level M. Standard choice when the reader and environment are both good.
50%	IATA BCBP, transit tickets, crumpled paper	Survives a folded corner or a significant smudge. IATA's implicit default.
75%–95%	High-abrasion or high-fold environments	Payload capacity drops sharply. Only for specialist use.

IATA BCBP format — Aztec's canonical use

The International Air Transport Association's Type M1 Bar Coded Boarding Pass is the single largest Aztec application by volume — billions of codes per year. The payload is a fixed-position ASCII string with these leading fields:

M1{PASSENGER/NAME}E{BOOKING_REF} {FROM} {TO} {AIRLINE} {FLIGHT} {DAY}{COMPARTMENT}{SEAT}{CHECK_IN_SEQ}{PASSENGER_STATUS}

M1 — format indicator (always M1 for single-segment).
PASSENGER/NAME — surname/given, padded with spaces to 20 chars.
E — electronic ticket indicator.
BOOKING_REF — 6-char PNR (passenger name record).
FROM/TO — 3-letter IATA airport codes (DEN, LHR, NRT…).
AIRLINE — 3-char carrier code (UA, BA, JL…).
DAY — Julian day of year (001–366).
COMPARTMENT — class of travel (F/J/Y/…).

Canonical test vectors

Case	Payload	Expected substring
Short URL	`https://example.com/board/AB12`	`example.com/board/AB12`
IATA BCBP minimal	`M1DOE/JOHN EABC123 JFKLHRBA 0100 042Y034A0001 100`	`M1DOE/JOHN`
Transit ticket with segment metadata	`M1SMITH/JANE EXYZ789 LAXSFOVA 0250 032Y012C0015 147`	`M1SMITH/JANE`

Common pitfalls

Consumer phone cameras don't decode Aztec. iPhone Camera returns nothing. Most Android cameras do the same. If your audience is the general public with a phone, use QR and accept lower density. Aztec is for dedicated readers (airport gates, turnstile scanners, OEM industrial imagers).
ECC 5% is a trap. The minimum legal ECC produces codes that fail on any crumple, glare, or abrasion. 23% is the safe floor; 50% is the production default for anything that will be printed on paper.
BCBP Type M1 vs M2. M1 is single-segment; M2 is multi-segment (up to 4 flights in one code). Verify your airline's gate readers support M2 before embedding multiple segments — some older readers reject it.
No position markers — rotation is handled but perspective isn't. Aztec tolerates rotation but NOT heavy perspective distortion. Scan from roughly perpendicular to the surface; 30°+ tilt degrades decoding.
Styling disabled. QR-specific features (custom dot shapes, gradients, centre logo) don't apply to Aztec. Abundera's Style panel disables itself for this type — see the capability banner on the Aztec generator.
Module pitch for print. Aztec needs at least 0.33 mm/module for reliable laser-scanner decoding; 0.5 mm for phone-camera reads on large-format Aztec tickets.

Scanner compatibility

Reader	Aztec support	Notes
iOS Camera (iOS 15+)	No	Apple has not added Aztec to the native Camera app. Third-party apps with Scandit or Dynamsoft SDKs work.
Android Camera (Google/Pixel)	Partial	Some OEM camera apps decode; Pixel stock camera does not reliably.
Google Lens	Unreliable	Decodes boarding-pass Aztec inconsistently. Not a viable verification path for production.
Zebra / Honeywell / Datalogic industrial imager	Yes	Every industrial 2D imager supports Aztec out of the box.
Airline / transit gate reader	Yes (canonical)	This is what Aztec was designed for. Every airport and rail gate reads Aztec reliably.
Scandit / Dynamsoft SDK	Yes	Used by most self-service kiosks and airline check-in apps.