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Swift Codable · dpearson2699 | DecimalAI

codingby dpearson2699

Swift Codable

dpearson2699/swift-codable

Source dpearson2699/swift-ios-skills ↗License NOASSERTION

Implement Swift Codable models for JSON and property-list encoding and decoding with JSONDecoder, JSONEncoder, CodingKeys, and custom init(from:) or encode(to:).

SkillScore95Maintained

Automatic

Coding pack

Last verified 8/14/2026

What it changes

Passed 21 of 22 test cases with the skill, and 20 of 22 without it.

Without skill91%

With skill95%

Checks it passed that the model alone missed

States that lossy decoding should only be used when partial array success is an explicit contract requirement.

1 fixed20 passed either way1 still failing0 broke

Pass-rate lift: +5 pp
Tokens: +153%
Agent turns: 0%
Response time: -34%

Model gemini-3.6-flashMeasured 8/14/2026v121 of 22 cases passed with skill

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/dpearson2699-swift-codable/SKILL.md https://app.decimal.ai/s/dpearson2699-swift-codable/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add dpearson2699-swift-codable, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/dpearson2699-swift-codable/ and pins it in .decimal/skills.lock

decimalai skills add dpearson2699-swift-codable

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/dpearson2699-swift-codable/SKILL.md https://app.decimal.ai/s/dpearson2699-swift-codable/SKILL.md

Raw file: /s/dpearson2699-swift-codable/SKILL.md ↗ · machine-readable summary at /s/dpearson2699-swift-codable.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

A test case the skill fixed. Same model, same prompt, with and without the skill.

Prompt

In Swift JSON decoding, when is it appropriate to catch decoding errors per item and skip bad elements in an array, rather than failing the entire decoding operation?

What was checked, without and with the skill
Checked	Without skill	With skill
States that lossy decoding should only be used when partial array success is an explicit contract requirement.	Missed	Passed

case-15 · gemini-3.6-flash · 8/14/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md345 lines2 files

Swift Codable

Encode and decode Swift types using Codable (Encodable & Decodable) with JSONEncoder, JSONDecoder, and related APIs. Targets Swift 6.3 / iOS 26+.

Decode and Verify Workflow
Basic Conformance
Custom CodingKeys
Custom Decoding and Encoding
Nested and Flattened Containers
Heterogeneous Arrays
Date Decoding Strategies
Data and Key Strategies
Lossy Array Decoding
Single Value Containers
Default Values for Missing Keys
Encoder and Decoder Configuration
Codable with URLSession
Codable with SwiftData
Codable with UserDefaults
Common Mistakes
Review Checklist
References

Decode and Verify Workflow

Decode representative success, missing, null, malformed, acronym-key, and date fixtures.
On failure, inspect DecodingError, its codingPath, and the raw payload.
Correct only the mismatched model, key, container, or strategy; do not hide contract failures with lossy decoding.
Rerun fixtures and encode/decode round trips where both directions are part of the contract.

Basic Conformance

When all stored properties are themselves Codable, the compiler synthesizes conformance automatically:

Track record

Benchmark

21 / 22

test cases passed, vs 20 / 22 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

dpearson2699 / swift-ios-skills

skills/swift-codable/SKILL.md

View on GitHub ↗

License NOASSERTIONImported 8/3/2026Version v1Bundled 1 file

More skills from the same source and nearby in the registry, with their headline benchmark lift.

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See it in action

What's inside

Swift Codable

Contents

Decode and Verify Workflow

Basic Conformance

Track record

Benchmark

Adoption

SkillSafety

Source

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