claude-skills is a collection of specialized skills that extends Claude Code for full-stack development. Developers use it for programming languages, frameworks, infrastructure, APIs, testing, DevOps, security, data and machine learning, platform tasks, and project workflows.
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 Jeffallan/claude-skills --skill kotlin-specialistgit clone --depth 1 https://github.com/Jeffallan/claude-skillsWrote 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/jeffallan/claude-skills/kotlin-specialist)<a href="https://agentmods.dev/skills/jeffallan/claude-skills/kotlin-specialist"><img src="https://agentmods.dev/badge/skills/jeffallan/claude-skills/kotlin-specialist/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/jeffallan/claude-skills/kotlin-specialist"><img src="https://agentmods.dev/badge/skills/jeffallan/claude-skills/kotlin-specialist.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk pass
- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Data Exfiltration · line 103 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
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 | $0.00086 | $0.01369 |
| Opus 5 | $0.00043 | $0.00685 |
| Sonnet 5 | $0.00017 | $0.00274 |
| Haiku 4.5 | $0.00009 | $0.00137 |
Grade A, and why
kotlin-specialist scanned grade A with 0 findings 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 13d 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.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
Copies of this mod
3 near-identical copies found in the catalogue:
- kotlin-specialist — 94% identical, 2 lines differ
- kotlin-specialist — 94% identical, 2 lines differ
- kotlin-specialist — 86% identical, 22 lines differ
How it starts
The opening of the file, as written. The whole thing — 150 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Kotlin Specialist
Senior Kotlin developer with deep expertise in coroutines, Kotlin Multiplatform (KMP), and modern Kotlin 1.9+ patterns.
Core Workflow
- Analyze architecture - Identify platform targets, coroutine patterns, shared code strategy
- Design models - Create sealed classes, data classes, type hierarchies
- Implement - Write idiomatic Kotlin with coroutines, Flow, extension functions
- Checkpoint: Verify coroutine cancellation is handled (parent scope cancelled on teardown) and null safety is enforced before proceeding
- Validate - Run
detektandktlint; verify coroutine cancellation handling and null safety- If detekt/ktlint fails: Fix all reported issues and re-run both tools before proceeding to step 5
- Optimize - Apply inline classes, sequence operations, compilation strategies
- Test - Write multiplatform tests with coroutine test support (
runTest, Turbine)
Reference Guide
Load detailed guidance based on context:
| Topic | Reference | Load When |
|---|---|---|
| Coroutines & Flow | references/coroutines-flow.md |
Async operations, structured concurrency, Flow API |
| Multiplatform | references/multiplatform-kmp.md |
Shared code, expect/actual, platform setup |
| Android & Compose | references/android-compose.md |
Jetpack Compose, ViewModel, Material3, navigation |
| Ktor Server | references/ktor-server.md |
Routing, plugins, authentication, serialization |
| DSL & Idioms | references/dsl-idioms.md |
Type-safe builders, scope functions, delegates |
Key Patterns
Sealed Classes for State Modeling
sealed class UiState<out T> {
data object Loading : UiState<Nothing>()
data class Success<T>(val data: T) : UiState<T>()
data class Error(val message: String, val cause: Throwable? = null) : UiState<Nothing>()
}
// Consume exhaustively — compiler enforces all branches
fun render(state: UiState<User>) = when (state) {
is UiState.Loading -> showSpinner()
is UiState.Success -> showUser(state.data)
is UiState.Error -> showError(state.message)
}
What ships with it
5 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 13d ago First seen · 150 lines · 86 tokens per session scan A d27d8e173d52
kotlin-specialist is a skill published in the GitHub repository Jeffallan/claude-skills (11,426 stars, last pushed 1mo ago), licensed MIT. It adds 86 tokens to every session and 1,369 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
Other skills, from other repositories
swift-macos
Build native macOS apps with Swift 6.3 (latest: 6.3.3, bundled in Xcode 26.6, Jun 2026), SwiftUI, SwiftData, and macOS 26 Tahoe (26.6.2 current). Target macOS 14+ for SwiftData/@Observable, macOS 15+ for latest SwiftUI, macOS 26 for Liquid Glass and Foundation Models. Note Xcode 26.6 still bundles the macOS 26.5 SDK…
xcode-makefiles
Install strict Xcode Makefile tooling for iOS/macOS projects, including build/run/test scripts with AGENTNAME-based per-agent isolation under build/. Use when a project needs reproducible local CLI builds without full app scaffolding.
bootstrap-ios
Bootstrap agents for iOS, iPadOS, macOS, Swift, SwiftUI, SwiftData/Core Data, Swift Testing, Xcode build/test/debug, Simulator, App Intents, or XcodeBuildMCP work. Use before building, fixing, refactoring, QAing, or setting up Apple-platform repos, and when asked to load/install Ray's iOS skills or bootstrap iOS.
swift
Use when writing Swift for iOS, macOS, or server-side. Covers value semantics, optionals, protocol-oriented design, structured concurrency with async/await and actors, and SwiftUI state management.
swift-concurrency-6-2
Swift 6.2 Approachable Concurrency — single-threaded by default, @concurrent for explicit background offloading, isolated conformances for main actor types.
bootstrap-xcode-workspace
Create, adopt, extend, and align one Swift product workspace with app, extension, package, and service components under one permanent Xcode entrypoint.