bysquare

"PAY by square" is a national standard for QR code payments that was adopted by the Slovak Banking Association in 2013. It is incorporated into a variety of invoices, reminders and other payment regulations.

Why

It's simple, I couldn't find any free implementation of "PAY by square" standard, so I decided to create one and share it with the community to help individuals and businesses to create QR codes for their invoices.

Features

• Compatible with Slovak banking apps
• Support latest PAY by square standard (v1.2.0)
• Isomorphic Browser & Runtime-independent (Browser, Node.js, Bun, Deno)
• Compatible with any system language using C Foreign Function Interface (CFFI)

Specification Versions

The specifications, XSD schemas and terms of use are published by the Slovak Banking Association.

Pay BySquare

Specification	Valid since	TypeScript	Go
v1.1	2015-06-24	v1.0.0 – v3.0.0	v0.1.0
v1.2	2025-10-09	v3.1.0+	v0.2.0+

Invoice BySquare

Specification	TypeScript	Go
none	v4.0.0+	v0.4.0+

Implementations

This repository provides multiple language implementations of the PAY by square standard:

• TypeScript - Supports Browsers and any runtime Node.js, Bun, Deno
• Go - Native Go implementation with CLI tool and C-compatible FFI

Both implementations are fully compatible with each other and follow the same specification.

---
title: "Implementations Overview"
config:
  theme: neutral
  themeVariables:
    fontFamily: monospace
    fontSize: "10px"
---

flowchart LR
    subgraph Core["Core Implementations"]
        TS[TypeScript]
        GO[Go]
    end

    subgraph Runtime["Runtime"]
        TS --> Browser
        TS --> Node/Bun/Deno
    end

    TS & GO --> CLI[CLI encoder/decoder tools]


    subgraph Native["Runtime"]
        GO --> GO_LIB[Go Applications]
    end

    subgraph FFI["Universal via C FFI"]
        GO --> CFFI[libbysquare.so/dll]
        CFFI --> ANY[Java, Python, PHP, C#, Swift, Dart]
    end

    GO --> Artifacts[.rpm, .deb, CLI binaries]

    style TS            fill:#A5D8FF, stroke:#1976D2, stroke-width:1.5px
    style Browser       fill:#A5D8FF, stroke:#1976D2, stroke-width:1.5px
    style Node/Bun/Deno fill:#A5D8FF, stroke:#1976D2, stroke-width:1.5px

    style GO      fill:#A5EAFF, stroke:#00838F, stroke-width:1.5px
    style GO_LIB  fill:#A5EAFF, stroke:#00838F, stroke-width:1.5px
    style CFFI    fill:#A5EAFF, stroke:#00838F, stroke-width:1.5px

Using C FFI

The Go implementation provides a C-compatible Foreign Function Interface (FFI), allowing you to use the library from any language that supports C bindings.

Available examples:

• Java - Using the Foreign Function & Memory API (JDK 19+)
• C# - Using P/Invoke (DllImport)
• PHP - Using FFI extension
• Python - Using ctypes
• Swift - Using Swift's C interoperability
• Dart - Using dart:ffi

See FFI examples for setup and usage instructions.

How it works

Both Pay BySquare and Invoice BySquare share the same wire format and encoding pipeline. The only difference is in the header nibbles — BySquareType and DocType.

LZMA uncompressed content (data before compression):

---
title: "LZMA uncompressed data"
config:
  theme: neutral
---
packet-beta
0-31: "CRC32 Checksum"
32-63: "Serialized Data"
64-95: "(variable...)"

Pay BySquare

BySquareType	DocType	Document
0x00	0x00	Payment

Invoice BySquare

BySquareType	DocType	Document
0x01	0x00	Invoice
0x01	0x01	Proforma Invoice
0x01	0x02	Credit Note
0x01	0x03	Debit Note
0x01	0x04	Advance Invoice

QR code wire format (bytes passed to Base32Hex encoding):

---
config:
  theme: neutral
---
packet-beta
0-3: "BySquareType"
4-7: "Version"
8-11: "DocType"
12-15: "Reserved"
16-31: "Data Length"
32-63: "LZMA Body"
64-95: "(variable...)"

Encoding process:

---
config:
  theme: neutral
  themeVariables:
    fontFamily: monospace
    fontSize: "12px"
---

flowchart TB
    subgraph Header["Header Track"]
        H_INPUT["   Header Info     "]
        BS_HEAD["  BySquare Header  "]
    end

    subgraph Payload["Payload Track"]
        P_INPUT["  Serialized Data  "]
        CRC["   CRC32 Checksum  "]
        UNCOMPRESSED["  CRC32 + Payload  "]
        D_LEN["    Data Length    "]
        LZMA_COMP[" LZMA Compression  "]
        LZMA_STRIP[" Strip LZMA Header "]
        LZMA_BODY["     LZMA Body     "]
    end

    subgraph Assemble["Assemble"]
        COMBINED["  Combined Binary  "]
    end

    subgraph Encode["Encode"]
        B32H["     Base32Hex     "]
        QR["      QR Code      "]
    end

    H_INPUT --> BS_HEAD
    P_INPUT -.-> CRC
    CRC --> UNCOMPRESSED
    P_INPUT --> UNCOMPRESSED
    UNCOMPRESSED -.-> D_LEN
    UNCOMPRESSED --> LZMA_COMP
    LZMA_COMP --> LZMA_STRIP
    LZMA_STRIP --> LZMA_BODY

    BS_HEAD --> COMBINED
    D_LEN --> COMBINED
    LZMA_BODY --> COMBINED
    COMBINED --> B32H
    B32H --> QR

Related

• https://bysquare.com/
• https://github.com/matusf/pay-by-square
• https://github.com/mattbosak/bysquare_dart
• https://devel.cz/otazka/qr-kod-pay-by-square
• https://www.vut.cz/studenti/zav-prace/detail/78439
• https://bsqr.co/schema/