Koha System

MARC21 vs MARCXML vs MRK: Which Format Should You Use?

Understand the differences between MARC21 binary, MARCXML, and MRK files when preparing records for Koha.

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Libraries often encounter several MARC-related formats during migration: MARC21 binary, MARCXML, and MRK. They can represent similar catalogue data, but they are used in different workflows.

MARCReady supports all three as input formats and exports MARC21 binary and MARCXML for Koha import.

Quick comparison

Format Common extension Best for
MARC21 binary .mrc, .marc Standard library-system export and Koha import
MARCXML .xml, .marcxml XML workflows, integrations, and readable structured exchange
MRK .mrk MARCEdit review and editing workflows

MARC21 binary

MARC21 binary is the compact machine-readable MARC format commonly exported by library systems.

Use MARC21 binary when:

  • Your current ILS can export .mrc or .marc.
  • You are preparing records for Koha import.
  • You want the most common MARC migration format.
  • You are working with migration consultants or cataloguing tools.

MARC21 binary is efficient, but it is not easy to read in a normal text editor. Use MARCEdit or another MARC tool if you need to inspect it manually.

MARCXML

MARCXML represents MARC records in XML.

Use MARCXML when:

  • Your system exports XML-based MARC data.
  • You are working with APIs or integrations.
  • You want a structured format that is easier to inspect than binary MARC.
  • Your migration workflow specifically requests MARCXML.

MARCXML can be larger than MARC21 binary, but it is useful for system integrations and debugging.

MRK

MRK is a plain-text representation commonly associated with MARCEdit workflows.

Use MRK when:

  • You are reviewing records manually.
  • You are using MARCEdit.
  • You want a readable version of MARC data.
  • You need to inspect fields and subfields before conversion.

MRK is helpful for review, but Koha import workflows usually expect MARC or MARCXML rather than MRK directly.

Which format should you upload to MARCReady?

Use this order of preference:

  1. MARC21 binary if your system exports it.
  2. MARCXML if that is your best structured export.
  3. MRK if you are working from a MARCEdit workflow.
  4. CSV, Excel, TSV, or JSON if your system cannot export MARC.

Which format should you export from MARCReady?

For Koha import, use:

  • MARC21 binary (.mrc) for the standard import workflow.
  • MARCXML (.marcxml) if your Koha workflow or migration process uses XML.

If you are unsure, start with MARC21 binary and test with a small staged import in Koha.

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