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CoreSync is an Objective-C diff/patch framework that supports the JSONPatch specification.

First, CoreSync can efficiently calculate the difference (the deltas) between two NSDictionary objects (of which can be represented as JSON). This is the diff part of CoreSync, which is also known as a binary log.

The second part of CoreSync is the patch functionality. Once the diff is calculated, CoreSync can apply each patch transaction to the original dictionary, bringing it up-to-date.

It’s particularly useful for syncing (as the name suggests).

Note: I’m also working on a fully Swift version of CoreSync. I’m excited about it, but CoreSync leverages a significant amount of Objective-C’s dynamism, which Swift doesn’t provide.

How to Get Started

CoreSync is flexible, modular, and lightweight. It’s also extremely easy to use in your projects, and comes with no dependencies.

  • Download CoreSync.
  • Try it out by opening the Xcode project and running the tests via the CoreSyncTests target. CoreSyncTests.m also provides an easy example of how to use the framework.
  • Install it in your own project by simply adding the CoreSync folder into your target, and #import "CoreSync.h".


In the simplest case, suppose we have two NSDictionarys (or JSON blobs) A and B.


    "a" : "aValue1",
    "c" : "cValue1"


    "a" : "aValue2",
    "b" : "bValue1"

In this trivial example, we can calculate the delta ourselves. Three changes must take place for A to mirror B:

  1. Replace the value of key a from aValue1 to aValue2
  2. Remove key c
  3. Add key b with value bValue1

Now let’s have CoreSync calculate the delta (and print it as a JSON blob), knowing what output to expect:

#import "CoreSync.h"

NSDictionary* A = ...
NSDictionary* B = ...

NSString* JSONChanges = [CoreSync diffAsJSON:A :B];
NSLog(@"%@", JSONChanges);

As expected, this will print:

    "op" : "replace",
    "path" : "/a",
    "value" : "aValue2"
    "op" : "remove",
    "path" : "/c"
    "op" : "add",
    "path" : "/b",
    "value" : "bValue1"

With this JSON diff, we can now patch A and verify that A and B are now identical in value:

A = [CoreSync patch:A withJSON:JSONChanges];
assert([A isEqualToDictionary:B]);

Obviously, CoreSync will also efficiently and intelligently handle complex diffs, nested collections, value type changes, and more. It’s pretty powerful!


  • If you need help, just ask! Email and Twitter both work.
  • If you found a bug, or have a feature request, open an issue.
  • If you would like to contribute, that’s awesome! Open up a pull request!

Enjoy! :octocat:


CoreSync is an elegant Objective-C diff/patch library for JSON and NSDictionaries.




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