Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add dagba/ios-mcp --skill swiftdata-coredata-persistencegit clone --depth 1 https://github.com/dagba/ios-mcpWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/dagba/ios-mcp/swiftdata-coredata-persistence)<a href="https://agentmods.dev/skills/dagba/ios-mcp/swiftdata-coredata-persistence"><img src="https://agentmods.dev/badge/skills/dagba/ios-mcp/swiftdata-coredata-persistence.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00038 | $0.02818 |
| Opus 5 | $0.00019 | $0.01409 |
| Sonnet 5 | $0.00008 | $0.00564 |
| Haiku 4.5 | $0.00004 | $0.00282 |
Grade A, and why
swiftdata-coredata-persistence scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 8d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
let items = try context.fetch(FetchDescriptor<OldSchema.Product>()) How it starts
The opening of the file, as written. The whole thing — 370 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SwiftData & CoreData Persistence
Overview
SwiftData and CoreData are NOT interchangeable. Each has specific strengths, migration traps, and performance patterns. Wrong framework choice or migration strategy causes production crashes.
Core principle: Choose framework based on app constraints, version models from day one, never store BLOBs in the database.
Framework Selection
digraph framework_choice {
"New iOS app?" [shape=diamond];
"iOS 17+ only?" [shape=diamond];
"Simple data model?" [shape=diamond];
"iCloud sync?" [shape=diamond];
"Existing CoreData?" [shape=diamond];
"Use SwiftData" [shape=box, style=filled, fillcolor=lightgreen];
"Use CoreData" [shape=box, style=filled, fillcolor=lightblue];
"Stay with CoreData" [shape=box, style=filled, fillcolor=lightblue];
"New iOS app?" -> "iOS 17+ only?" [label="yes"];
"New iOS app?" -> "Existing CoreData?" [label="no"];
"Existing CoreData?" -> "Stay with CoreData" [label="yes"];
"Existing CoreData?" -> "iOS 17+ only?" [label="no"];
"iOS 17+ only?" -> "Simple data model?" [label="yes"];
"iOS 17+ only?" -> "Use CoreData" [label="no"];
"Simple data model?" -> "iCloud sync?" [label="yes"];
"Simple data model?" -> "Use CoreData" [label="no"];
"iCloud sync?" -> "Use SwiftData" [label="yes"];
"iCloud sync?" -> "Use SwiftData" [label="no"];
}
Choose SwiftData When
- New app, iOS 17+ deployment target
- Simple relationships (mostly 1:1 or 1:N, few complex queries)
- SwiftUI-first architecture
- iCloud sync needed with minimal configuration
Choose CoreData When
- iOS 16 or earlier support required
- Complex queries with NSCompoundPredicate, subqueries
- UIKit-heavy app with NSFetchedResultsController
- Existing CoreData codebase (migration complex, stay with CoreData)
- Performance critical (as of 2025, CoreData still faster)
- Abstract entities or inheritance hierarchies
Migration Death Traps
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 8d ago First seen · 370 lines · 38 tokens per session scan A 6bd7c3b01b0e
swiftdata-coredata-persistence is a skill published in the GitHub repository dagba/ios-mcp (3 stars, last pushed 7mo ago), licensed MIT. It adds 38 tokens to every session and 2,818 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
Other skills, from other repositories
setup-datamodel
Use when the user wants to design or redesign the Dataverse schema and connector plan for an existing mobile app, or has an ER diagram (image, Mermaid, or text) to apply. Skip when the user is creating a brand-new app — /create-mobile-app handles the data model inline.
axiom-audit-swiftdata
Use when the user mentions SwiftData review, @Model issues, SwiftData migration safety, or SwiftData performance checking.
axiom-audit-core-data
Use when the user mentions Core Data review, schema migration, production crashes, or data safety checking.
firebase-database
Use when syncing real-time data, structuring JSON trees, reading/writing, creating listeners, enabling offline persistence, managing presence, sharding, or writing security rules.
axiom-data
Use when working with ANY data persistence, database, storage, CloudKit, migration, or serialization. Covers SwiftData, Core Data, GRDB, SQLite, Realm, CloudKit sync, file storage, Codable, migrations.
android-data-layer
Guidance on implementing the Data Layer using Repository pattern, Room (Local), and Retrofit (Remote) with offline-first synchronization.