swift-codable-json

Decode and encode Swift JSON with Codable and CodingKeys.

3|2|Updated Jan 18, 2026
One-click install
npx skills add https://github.com/dagba/ios-mcp --skill swift-codable-json
Or copy as Structured Prompt for Agent
Please help me install this Agent Skill.
Skill: swift-codable-json
Source: https://github.com/dagba/ios-mcp/tree/main/skills/swift-codable-json
Command: npx skills add https://github.com/dagba/ios-mcp --skill swift-codable-json

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Codable provides strong typing for JSON parsing but APIs often return mismatched or nested data, date formats vary, and keys use snake_case. This skill guides you in designing robust Swift models that decode API responses reliably and fail gracefully when data is missing or malformed.

Core Features & Use Cases

  • Handle snake_case to camelCase mappings with CodingKeys for every renamed property, ensuring stable decoding across API versions.
  • Decode nested JSON structures into flat, strongly-typed Swift models using nested containers and CodingKeys.
  • Manage multiple date formats in the same response with custom decoding logic or dedicated date properties, improving resilience in real-world APIs.
  • Provide safe optional fields with decodeIfPresent and sensible defaults to prevent runtime crashes.
  • Use clear, testable error handling patterns to surface decoding failures with actionable diagnostics.

Quick Start

Define a Codable model, customize keys as needed, and decode from JSON data. For example, create a struct matching the API, implement a CodingKeys enum or a custom init(from:), and then use JSONDecoder().decode(YourModel.self, from: jsonData) to obtain a typed instance.

Frequently Asked Questions about swift-codable-json

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

FAQPage Schema
How do I decode nested JSON structures into flat Swift Codable models?

Decode nested JSON structures into flat Swift models using nested containers and CodingKeys within a custom init(from:) to map deeply nested API responses to strongly-typed properties safely.

How do I map snake_case JSON keys to camelCase properties in Swift?

Map snake_case JSON keys to camelCase properties in Swift by defining a CodingKeys enum that explicitly matches each API response key to your strongly-typed Codable model properties for stable decoding.

What's the best way to handle multiple date formats in a single Swift JSON response?

Handle multiple date formats in a single Swift JSON response by implementing custom decoding logic or dedicated date properties within init(from:) to parse varying date strings reliably without crashing.

How do I safely decode optional fields in Swift Codable without runtime crashes?

Safely decode optional fields in Swift Codable by using decodeIfPresent to provide sensible defaults for missing or malformed JSON keys, preventing runtime crashes during API response parsing.

Why does my Swift JSONDecoder fail when data is missing or malformed?

Swift JSONDecoder fails when data is missing or malformed because standard decoding expects exact type matches. Implement custom init(from:) with structured error handling to surface actionable diagnostics and fail gracefully.

Does Swift Codable work with varying API versions that change key names?

Swift Codable handles varying API versions that change key names by using CodingKeys to map every renamed property explicitly, ensuring stable decoding across different API response structures.