Amethyst is an Android client for Nostr, a social network protocol that lets people control their own social activity and connections. People use it to read and publish Nostr content, follow accounts, and exchange encrypted direct messages from Android and other supported platforms. The catalogue add-ons support workflows for developing or operating the client.
Borrowing it
Nothing to install: this file belongs to vitorpamplona/amethyst. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/vitorpamplona/amethyst/main/.claude/skills/kotlin-multiplatform/SKILL.mdgit clone --depth 1 https://github.com/vitorpamplona/amethystWrote 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/vitorpamplona/amethyst/kotlin-multiplatform)<a href="https://agentmods.dev/skills/vitorpamplona/amethyst/kotlin-multiplatform"><img src="https://agentmods.dev/badge/skills/vitorpamplona/amethyst/kotlin-multiplatform/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/vitorpamplona/amethyst/kotlin-multiplatform"><img src="https://agentmods.dev/badge/skills/vitorpamplona/amethyst/kotlin-multiplatform.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk warn
- NVIDIA SkillSpector pass
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 | $0.00119 | $0.03341 |
| Opus 5 | $0.00060 | $0.01670 |
| Sonnet 5 | $0.00024 | $0.00668 |
| Haiku 4.5 | $0.00012 | $0.00334 |
Grade A, and why
kotlin-multiplatform 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 9d 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.
How it starts
The opening of the file, as written. The whole thing — 403 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Kotlin Multiplatform: Platform Abstraction Decisions
Expert guidance for KMP architecture in Amethyst - deciding what to share vs keep platform-specific.
When to Use This Skill
Making platform abstraction decisions:
- "Should I create expect/actual or keep Android-only?"
- "Can I share this ViewModel logic?"
- "Where does this crypto/JSON/network implementation belong?"
- "This uses Android Context - can it be abstracted?"
- "Is this code in the wrong module?"
- Preparing for iOS/web/wasm targets
- Detecting incorrect placements
Abstraction Decision Tree
Central question: "Should this code be reused across platforms?"
Follow this decision path (< 1 minute):
Q: Is it used by 2+ platforms?
├─ NO → Keep platform-specific
│ Example: Android-only permission handling
│
└─ YES → Continue ↓
Q: Is it pure Kotlin (no platform APIs)?
├─ YES → commonMain
│ Example: Nostr event parsing, business rules
│
└─ NO → Continue ↓
Q: Does it vary by platform or by JVM vs non-JVM?
├─ By platform (Android ≠ iOS ≠ Desktop)
│ → expect/actual
│ Example: Secp256k1Instance (uses different security APIs)
│
├─ By JVM (Android = Desktop ≠ iOS/web)
│ → jvmAndroid
│ Example: Jackson JSON parsing (JVM library)
│
└─ Complex/UI-related
→ Keep platform-specific
Example: Navigation (Activity vs Window too different)
Final check:
Q: Maintenance cost of abstraction < duplication cost?
├─ YES → Proceed with abstraction
└─ NO → Duplicate (simpler)
Real Examples from Codebase
Crypto → expect/actual:
// commonMain - expect declaration
expect object Secp256k1Instance {
fun signSchnorr(data: ByteArray, privKey: ByteArray): ByteArray
}
// androidMain - uses Android Keystore
// jvmMain - uses Desktop JVM crypto
// iosMain - uses iOS Security framework
Why: Each platform has different security APIs.
JSON parsing → jvmAndroid:
// quartz/build.gradle.kts
val jvmAndroid = create("jvmAndroid") {
api(libs.jackson.module.kotlin)
}
Why: Jackson is JVM-only, works on Android + Desktop, not iOS/web.
What ships with it
6 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.
- 9d ago First seen · 403 lines · 119 tokens per session scan A 355a91b8d9f5
kotlin-multiplatform is a skill published in the GitHub repository vitorpamplona/amethyst (1,596 stars, last pushed today), licensed MIT. It adds 119 tokens to every session and 3,341 once invoked, about $0.0006 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.
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