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 agentmods add skills/heapy/kortex/modern-kotlinnpx skills add Heapy/kortex --skill modern-kotlingit clone --depth 1 https://github.com/Heapy/kortexWrote 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/heapy/kortex/modern-kotlin)<a href="https://agentmods.dev/skills/heapy/kortex/modern-kotlin"><img src="https://agentmods.dev/badge/skills/heapy/kortex/modern-kotlin.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 | $0.00150 | $0.04372 |
| Opus 5 | $0.00075 | $0.02186 |
| Sonnet 5 | $0.00030 | $0.00874 |
| Haiku 4.5 | $0.00015 | $0.00437 |
Grade A, and why
modern-kotlin 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 4d 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.
It earns its place only when the failure has to outlive the block: `urls.map { runCatching { fetch(it) } }`, How it starts
The opening of the file, as written. The whole thing — 303 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Modern Kotlin
Use this skill to write idiomatic Kotlin with the features added in the last four years (mid-2022 → 2026, Kotlin 1.7 → 2.4.20-Beta1) and to know exactly which compiler flag or opt-in each preview feature needs.
State as of July 2026:
- Latest stable: 2.4.10 (July 14, 2026). EAP: 2.4.20-Beta1 (2.4.20 final planned September 2026).
- Default language version is 2.4. K1 is gone: 2.4.0 dropped
-language-version 1.9; K2 has been the only compiler since 2.0.0 (May 2024). - Context receivers (
-Xcontext-receivers) were removed in 2.3.20 — always migrate to context parameters.
Detailed per-version notes with full stdlib/tooling changes live in references/ (linked at the bottom). Older
pre-2022 features (sealed interfaces, value classes, fun interface, Duration API, …) are in
references/kotlin-1.4-1.6.md.
Release timeline
| Version | Date | Language headliners |
|---|---|---|
| 1.7.0 / 1.7.20 | Jun / Sep 2022 | K2 Alpha; builder inference, T & Any, opt-in stable; ..< and data object previews |
| 1.8.0 / 1.8.20 | Dec 2022 / Apr 2023 | old JVM backend removed; Enum.entries preview, Base64/AutoCloseable experimental |
| 1.9.0 / 1.9.20 | Jul / Nov 2023 | entries, data object, ..<, time API stable; K2 Beta; KMP stable |
| 2.0.0 / 2.0.20 | May / Aug 2024 | K2 stable, smart-cast upgrades; copy() visibility migration; Uuid |
| 2.1.0 / 2.1.20 | Nov 2024 / Mar 2025 | previews: guard conditions, non-local break/continue, $$ interpolation; atomics, Instant |
| 2.2.0 / 2.2.20 | Jun / Sep 2025 | guards + $$ + non-local break/continue stable; context parameters preview; contracts previews |
| 2.3.0 / 2.3.20 | Dec 2025 / Mar 2026 | return-value checker, explicit backing fields; name-based destructuring; context receivers removed |
| 2.4.0 | Jun 3, 2026 | context parameters stable, collection literals, @IntroducedAt; K1 dropped |
| 2.4.10 | Jul 14, 2026 | bug fixes only — current stable |
| 2.4.20-Beta1 | Jun 24, 2026 | explicit context arguments stable; when via invokedynamic default (JVM 21+) |
What ships with it
8 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.
- 4d ago First seen · 303 lines · 150 tokens per session scan A fce20223f7ec
modern-kotlin is a skill published in the GitHub repository Heapy/kortex (6 stars, last pushed 6d ago), licensed Apache-2.0. It adds 150 tokens to every session and 4,372 once invoked, about $0.0007 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.
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