The unofficial MDB Guide

Tech Specs for the JET format used by Access 1997-2010

The goal of this guide is to document everything I know about the different versions of the JET file format. Right now this is work in progress, and it probably will remain work in progress for an indeterminate time. I am updating stuff as I'm working on it, but I have no plans on actually finishing this guide.

JET is the file format used by Microsoft Access' MDB and ACCDB databases. These databases are ubiquitous in the Windows world. The file format is used not only by Access, but also as an underlying storage engine by countless third party apps. Unfortunately (but also quite understandably) Microsoft does not provide an open source implementation or a detailed technical specification.



I found out most of what I know about the MDB file format from various sources around the internet. I would like to thank everyone who shared their knowledge with the world. Here are the most important sources I used:

I have discovered a lot of the information documented here myself, by experimenting and staring at HEX code for hours. Special thanks goes to ridiculous_fish for the free hex editor Hex Fiend.