NEW: Nominations are now open for the 2019 Swift Community Awards! >>

How to convert between camel case and snake case with Codable and keyEncodingStrategy

Swift version: 5.1

Paul Hudson    @twostraws   

Most Swift developers use camel case for naming properties, which means we start with a lowercase letter then capitalize the first letter of second and subsequent words: numberOfUsers or powerLevel. On the other hand, many web APIs prefer snake case, written as number_of_users and power_level, so if you need to convert camel case to snake case you need to use the keyEncodingStrategy of JSONEncoder, like this:

let encoder = JSONEncoder()
encoder.keyEncodingStrategy = .convertToSnakeCase

if let encoded = try? encoder.encode(yourData) {
    // continue with encoded data

With that set, Swift can convert property names as part of the encoding process, which makes Codable much easier to use.

A similar property exists on JSONDecoder, except now it’s called keyDecodingStrategy. It does the same thing in reverse: specifying .convertFromSnakeCase will convert names_like_this into namesLikeThis.

LEARN SWIFTUI FOR FREE I have a massive, free SwiftUI video collection on YouTube teaching you how to build complete apps with SwiftUI – check it out!

Available from iOS 8.0

Similar solutions…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!