JSON to Objective-C Converter Online

Hand-rolling Objective-C model headers from a long REST API payload is monotonous and bug-prone — a single mistyped @property name silently nulls a field at runtime under reflection-based mappers. OpenFormatter's converter walks the JSON tree once, generates idiomatic Objective-C, and runs entirely in your browser so internal API responses never leave your machine.

How to generate Objective-C from JSON — 4 steps

1. Paste a real JSON response. Use a representative sample — the type inference quality depends on it. Booleans must be true/false, numbers must be unquoted.
2. Click Convert. The tool emits a Root @interface plus one separate interface per nested object, with strong/assign property attributes.
3. Copy and paste into Xcode. Each interface goes into its own .h file; create matching .m stubs with empty @implementation blocks.
4. Deserialize. Use NSJSONSerialization to parse, then assign each NSDictionary key to its matching property — or hand the dictionary to a model framework like Mantle for automatic mapping.

JSON to Objective-C type mapping

{
  "id": 42,
  "name": "Ada Lovelace",
  "active": true,
  "score": 98.5,
  "address": { "city": "London" },
  "tags": ["admin", "engineer"]
}

#import <Foundation/Foundation.h>

@interface Root : NSObject
@property (nonatomic, strong) NSNumber *id;
@property (nonatomic, strong) NSString *name;
@property (nonatomic, assign) BOOL active;
@property (nonatomic, strong) NSNumber *score;
@property (nonatomic, strong) Address *address;
@property (nonatomic, strong) NSArray *tags;
@end

@interface Address : NSObject
@property (nonatomic, strong) NSString *city;
@end

Common use cases

• check_circleGenerating Objective-C model headers for a legacy iOS app still primarily written in Objective-C
• check_circleProducing Cocoa data classes when bridging from a Swift module that consumes a REST API
• check_circleModelling NSDictionary payloads returned from NSJSONSerialization into typed @interface objects
• check_circleBuilding Mantle MTLModel base classes with auto-generated @property declarations
• check_circleGenerating headers for JSONModel or YYModel base classes that map dictionaries via runtime reflection
• check_circleModelling internal SDK responses that have not yet been ported to Swift Codable
• check_circleProducing CocoaPods library data models from a published JSON spec
• check_circleMaintaining macOS apps that still rely on AppKit + Foundation Objective-C frameworks

Why client-side generation matters

The JSON you paste often contains real customer data, OAuth tokens, signed URLs, or internal field names you do not want indexed by a third-party converter. OpenFormatter generates the Objective-C entirely in JavaScript on your device — open the Network tab in DevTools and you will see zero requests when you click Convert. Safe for enterprise iOS work, safe behind a corporate proxy, safe when the API contract is itself confidential.