swift-codable

Encode and decode Swift types with Codable using JSONEncoder and JSONDecoder.

Updated Apr 19, 2026

Search Tags:#json #swift #encoding #decoding #codable #codingkeys #urlsession

Ready to run

npx skills add https://github.com/femitz/flyby --skill swift-codable-femitz

💬 Prompt for ChatGPT / Claude Chat▼

Please help me install this Agent Skill.
Skill: swift-codable
Source: https://github.com/femitz/flyby/tree/main/.agents/skills/swift-codable
Command: npx skills add https://github.com/femitz/flyby --skill swift-codable-femitz

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Swift projects often struggle with robust and consistent encoding/decoding between JSON or plist data and strongly-typed models. This Skill provides a comprehensive guide to using Codable for reliable round-tripping and interop with URLSession, SwiftData, or UserDefaults.

Core Features & Use Cases

Basic conformance and automatic synthesis when all properties are Codable.
Custom CodingKeys and custom init(from:) / encode(to:) to map API responses, flatten nested JSON, date or data decoding strategies, and integration with URLSession, SwiftData, and UserDefaults for end-to-end data flows.
Use cases include API integration, local storage, and data mutations with nested or optional values.

Quick Start

Create a Swift struct that models a sample JSON payload and decode it with JSONDecoder.

Frequently Asked Questions about swift-codable

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I decode JSON responses into Swift types using Codable?▼

To decode JSON into Swift types, define a struct conforming to Codable and use JSONDecoder to parse the data payload into strongly-typed models for reliable data access.

How do I map nested JSON keys to Swift struct properties with CodingKeys?▼

CodingKeys map nested JSON keys to Swift struct properties by defining custom enums for custom init(from:) and encode(to:) to flatten nested structures and handle optional values.

How do I configure date decoding strategies in JSONDecoder for API integration?▼

Date decoding strategies in JSONDecoder can be configured to handle ISO8601 or custom formats when parsing API responses, ensuring reliable round-tripping of date values in Swift models.

Can I use Codable with URLSession, SwiftData, and UserDefaults for local storage?▼

Yes, Codable works with URLSession, SwiftData, and UserDefaults to provide end-to-end data workflows, enabling seamless encoding and decoding for API integration and local storage.

Why does decoding fail when optional values are missing in the JSON payload?▼

Decoding fails when required properties are missing or types mismatch, but using optional properties in your Codable structs allows graceful handling of missing keys in the JSON payload.

What's the best way to handle custom JSON encoding and decoding in Swift?▼

The best way to handle custom encoding in Swift is implementing custom init(from:) and encode(to:) methods to transform data and apply specific strategies for complex API response mapping.