What is the Online Cash Register Log Query System (OPF)?

The Online Cash Register Log Query System (Hungarian acronym: OPF) is a machine-to-machine (M2M) digital service provided by the National Tax and Customs Administration of Hungary (NAV). Launched in 2023, the system allows businesses to automatically retrieve the latest transaction logs and operational records submitted by their online cash registers to NAV.

Its purpose is to enhance transparency, ensure data traceability, and support businesses in self-auditing and tax administration.

What is the OPF system used for?

Through the OPF system, taxpayers can:

• Retrieve the most recent transmission timestamp of their online cash registers,
• Access the latest log files sent from the registers to NAV.

This service is particularly useful for:

• Accountants and financial managers tracking daily transactions,
• IT administrators or service technicians troubleshooting issues,
• Businesses pre-validating data before a possible tax inspection.

How does the OPF system work?

The OPF system operates via a machine-to-machine (M2M) interface. To use it:

• The taxpayer must create a technical user in the NAV Online Invoice System.
• Using that user’s credentials, an automated query can be executed via API, allowing access to:
• The list of online cash registers registered under the given tax number,
• The timestamp of the most recent transaction,
• The content of the most recently submitted log files.

The OPF system is not designed for manual use, but rather for integration into enterprise systems such as ERPs or POS backends.

What are the benefits of the OPF system?

• Real-time visibility of cash register operations,
• Detection of anomalies (e.g. a device not transmitting data for an extended period),
• Supports proactive internal audits, even before a NAV inspection occurs,
• Fully automatable and integrable into enterprise software environments.

How does OPF differ from other NAV-related systems?

System Purpose Access Type Intended Users
Online cash register Real-time data reporting to NAV Automatic via mobile data NAV, taxpayers
eCash register eReceipt issuance + transmission Web/M2M interface Digital retailers
OPF system Log file and transaction retrieval Technical user + API IT admins, accountants

Who can use the OPF system?

To use OPF, the following are required:

• A business registered with NAV operating at least one online cash register,
• A technical user set up in the Online Invoice system,
• Ability to make automated API calls (e.g. via REST interface).
• Use of the system is voluntary, but strongly recommended for compliance assurance and internal monitoring.

Summary

The Online Cash Register Log Query System (OPF) is a digital tool developed by NAV that allows taxpayers to retrieve transaction logs and operational data previously submitted from their online cash registers. Available widely since 2023, it supports self-auditing, error detection, and improved financial oversight. OPF is part of NAV’s broader move toward a more transparent and digitized tax environment.

Official definition

The OPF system is a machine-to-machine interface provided by NAV, enabling the retrieval of log files and transaction events submitted by online cash registers. Use requires a technical user created within the NAV Online Invoice system.”

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