SKILL.md
JetBrains IDE VM Options
Generate .vmoptions configurations for JetBrains IDEs. Output as Markdown code blocks (one option per line, # comments). Do not generate files directly.
Workflow
1. Identify IDE version (blocking)
Read [prerequisite-check.md](references/prerequisite-check.md) for validation logic. IDE version determines the JDK (17 vs 21), which controls which GC collectors and flags are available. Never skip this step — wrong version means wrong recommendations.
2. Understand the user's goal
Match the user's problem to a tuning strategy:
| User says | Primary goal | Start with |
|---|---|---|
| "freezes", "hangs", "lag", "UI stutter" | Low GC pause times | [gc-options.md](references/gc-options.md) → ZGC/Shenandoah |
| "slow indexing", "build is slow" | Throughput | [gc-options.md](references/gc-options.md) → G1GC/Parallel |
| "out of memory", "OOM", "large project" | Memory capacity | [memory-options.md](references/memory-options.md) → heap sizing |
| "startup is slow" | Fast startup | [common-options.md](references/common-options.md) → tiered compilation |
| "general tuning", "optimize" | Balanced | All references as needed |
3. Compose options from references
Read only the relevant reference files. Each reference includes flag descriptions, defaults, usage notes, and example configurations.
| File | Content | Read when |
|---|---|---|
| [prerequisite-check.md](references/prerequisite-check.md) | IDE version validation, JDK mapping | Always (step 1) |
| [gc-options.md](references/gc-options.md) | GC selection and tuning flags | GC-related goals |
| [memory-options.md](references/memory-options.md) | Heap, code cache, metaspace, large pages | Memory-related goals |
| [common-options.md](references/common-options.md) | Compiler, strings, diagnostics, threads | Performance/startup goals |
4. Self-review before presenting
- Verify every flag is compatible with the user's JDK version
- Remove flags that conflict with each other (e.g., two different GC activations)
- Remove flags the user didn't ask about and doesn't need — lean configs are better
- Include a brief comment explaining each section's purpose
5. Present with context
Show the final .vmoptions block with:
- A header comment noting the IDE version and JDK
- Grouped sections (Memory, GC, Performance, Diagnostics)
- A short explanation of each non-obvious choice
Scope
- Supported: IDE versions 222+ (JDK 17) and 243+ (JDK 21)
- GC collectors: Generational ZGC, ZGC, G1GC, Shenandoah, Parallel, Serial
- Tuning areas: Memory, code cache, metaspace, GC, compiler, strings, diagnostics
- Not in scope: OS-level tuning, plugin configuration, IDE settings (non-JVM), or IDE versions below 222
Output Example
# JetBrains IDE VM Options
# IntelliJ IDEA 2024.3 (version 243, JDK 21)
# Memory
-Xms2g
-Xmx4g
# Garbage Collector: Generational ZGC
-XX:+UseZGC
-XX:+ZGenerational
# Performance
-XX:ReservedCodeCacheSize=512m
-XX:+UseStringDeduplication
-XX:SoftRefLRUPolicyMSPerMB=50
# Diagnostics
-XX:+HeapDumpOnOutOfMemoryError
-XX:CICompilerCount=2