What is the MDB file format?
.mdb is a database file generated and used by Microsoft Access - it is the native format of this software, based on the Access Jet database engine. .mdb files contain data regarding databases: the structure and queries of a database, functions, records, and other information. Besides that, .mdb files can also store forms for entering data, module procedures, reports, and security settings.
Access data can be imported and joined with other formats and applications, such as HTML, XML, Excel, SharePoint, and Outlook. .mdb files can be converted to .csv or .txt using tools like MDB Converter or Access's built-in export wizard, so the data can be worked with in many other programs. Internally, an .mdb file begins with the bytes 00 01 00 00 followed at offset 4 by the ASCII string Standard Jet DB - a reliable identifier in a hex editor.
MDB files and their successor
.mdb was the default format in Microsoft Access 2003 and its previous versions. Newer versions of Access use a format that has replaced .mdb - the .accdb format (introduced in Access 2007). Current versions of Access can still open .mdb files, but .accdb adds multi-valued fields, attachment columns, and stronger encryption.
MDB and LDB
Along with .mdb files, in the same folder there can also be a file with the .ldb extension, because it is created by Access whenever an .mdb file is open. .ldb is a lock file created by the program the moment an .mdb file is being edited by a user. This prevents multiple users from introducing conflicting changes to the file at the same time. The .ldb file is removed automatically when the last user closes the database.
Security & safety
RISK: MEDIUMAn .mdb can contain VBA macros that run code, so a database from an untrusted source can carry malware - Access opens unknown databases with macros disabled (the Trust Center / yellow security bar), and you should leave them disabled unless you trust the sender. Beyond macros, the data itself is inert. Legacy security caveat: the old Jet "database password" and user-level (workgroup) security on .mdb are WEAK and easily bypassed/ cracked - never rely on them to protect sensitive data; the file content is effectively readable by tools like mdbtools regardless. Don't delete the .ldb lock file while the database is open in another session. Old .mdb files are also a corruption risk - keep backups and use Compact & Repair.
Format details
in a nutshellPrograms that open MDB files
Windows4 apps
Microsoft Access
Paid Double-click the .mdb to open it in Access (full read-write, forms, reports, VBA). Modern Access still opens legacy MDB. 
MDB Viewer Plus
Free Portable freeware (no install) - open the .mdb to view/edit tables and export to Excel/CSV/XML. The easiest free Windows opener. 
LibreOffice Base
Open-source Free office suite; connect to the .mdb to browse tables and run queries. Some forms/VBA won't carry over.
Microsoft Access Runtime
Free Free runtime that RUNS an Access app (forms/reports) but can't design it - for using an existing legacy database. 
macOS3 apps
LibreOffice Base
Open-source Best free Mac option - open the .mdb to view tables and export data. There is NO Microsoft Access for Mac. Complex queries/forms may not load.
MDB Tools (CLI / Homebrew)
Open-source 'brew install mdbtools', then 'mdb-tables file.mdb' and 'mdb-export file.mdb Table > out.csv' to extract data.
Parallels Desktop + Windows
Paid Run Windows (and real Access) in a VM on Mac when LibreOffice Base can't fully handle the database. 
Linux3 apps
MDB Tools
Open-source Command line: 'mdb-tables file.mdb' lists tables; 'mdb-export file.mdb TableName > out.csv' dumps to CSV; 'mdb-schema' dumps the schema.
LibreOffice Base
Open-source Open the .mdb to read tables and export; combine with mdbtools for command-line extraction.
Kexi (KEXI)
Open-source KDE database app - import/migrate Access .mdb tables (development is slow; use mdbtools/LibreOffice if it struggles). Technical details
deep spec| Developer | Microsoft Corporation |
| MIME type | application/x-msaccess |
| File signature | 00 01 00 00 at offset 0; ASCII "Standard Jet DB" at offset 4 |
| Database engine | Microsoft Jet 3.0 (Access 97) through Jet 4.0 (Access 2000-2003) |
| Page size | 2 048 bytes per page (Jet 3.x / Access 97); 4 096 bytes per page (Jet 4.0 / Access 2000-2003) |
| Maximum file size | 2 GB |
| Maximum fields per table | 255 |
| Unicode support | Compressed Unicode in Jet 4.0 (Access 2000+); code-page encoding in Jet 3.x (Access 97) |
| Embedded VBA | Compiled VBA p-code modules stored directly inside the file alongside table data |
| Password encryption | 40-bit RC4 cipher; known to be weak and susceptible to offline cracking |
| Lock file | A paired .ldb file is created on open; tracks active users and locked records; deleted when the last user closes |
| Successor format | .accdb (Access 2007+, ACE engine); identified by "Standard ACE DB" at offset 4; adds stronger encryption and attachment fields |
| Cross-platform tools | MDB Tools (mdb-export, mdb-tables) for Linux and macOS; LibreOffice Base and Kexi on Linux |
| Import/export connectors | Native support for Excel, SharePoint, Outlook, HTML, XML, and ODBC data sources |
| Maximum objects per database | 32 768 (tables, queries, forms, reports, and macros combined) |
| Released | 1992 (Access 1.0); MDB was the default through Access 2003 |
| Specification | learn.microsoft.com |
MDB conversions
Community Q&A
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